In Proto-Indo-European (PIE), it's easy to show that in some stage of Pre-IE, there was once a heavy stress accent (as in English or Italian) that caused unstressed vowels to erode and disappear altogether. In the later PIE stage, tonal accent is reconstructed. Pick any noun that shows accent alternation when declined and we can see the evidence of Syncope plain as day. The animate word *h₂éwis 'bird' (nominative case) is *h₂wei-s 'of the bird' in the genitive case, and likewise *ḱwōn-s 'dog' (nominative case) is *ḱun-ós in the genitive. The only sensible conclusion is that these forms were more regular further into the past. Hence we may infer that before Syncope, there was a vowel between the consonants of *h₂w- in genitive *h₂weis (say, *h₂VwéisV) and that *ḱun- in *ḱunós was originally something along the lines of *kVwVn-ósV, thereby matching the nominative and accusative forms which would have been the same shape but with accent on the preceding syllable.
In my theory, the stage preceding Syncope (i.e. Mid IE) appears to have a perfectly predictable accent which is always found on the penultimate syllable unless the word ends in any of a handful of suffixes originating from particles agglutinated sometime around early Mid IE (MIE). Antepenultimate accent is found in the nominative singular in *-sa becoming PIE *-s (from *sa 'the' > PIE *so 'this'), the 3ps verbal ending *-ta(i) becoming PIE *-t(i), (based on *ta 'that' > PIE *to-) and the pronominal inanimate in *-ta becoming *-d (also based on MIE *ta 'that'). I presume by Occam's Razor that all initial clusters in PIE dating to Mid IE were the product of Syncope until such time as it can be proven that some clusters were inherited from before Syncope (and I still haven't found any good reason to believe otherwise). By letting logical simplicity be my guide, this has given me a consistent and simple syllabic structure in MIE that allows only *CV(C) (where C = 'consonant' and V = 'vowel').
So this is all straight-forward and has been concluded by many people before me (such as the previously-mentioned linguist, C.H. Borgstrøm). However I'm dismayed that, whether it be Nostraticists who can't see the trees for the forest or conservative Indo-Europeanists (IEists) who can't see the forest for the trees, no one seems to have noticed what this event of Syncope inevitably implies beyond these more obvious examples.
We are soon confronted with a problem if, by chance, we allow our imagination to dream up a hypothetical word form for the sake of argument, something perhaps that doesn't behave so nicely as we would like. Let's say that there was an MIE verb root like **makéra-. As I've described MIE above, there is absolutely nothing objectionable about such a form. It's only when Syncope operates on it that we start to notice a snag since without any interference, we should expect **mker-. In fact, it's rather silly to expect such a thing because although almost anything is possible in languages around the world, a sequence like */mk-/ in a verb root is unheard of in PIE . We would expect perhaps that *m would remain syllabic somehow but verb roots in PIE simply don't look like this and conform to a stricter structure that disallows many shapes.
Therefore, since all sorts of run-of-the-mill sequences in MIE can lead us very easily to awkward consonant clusters when Syncope is applied, this one example illuminates for us that something more drastic must have happened in pre-IE. This 'something' is phonotactic restructuring which would reestablish sanity in the language's syllabicity despite the murderous deletion of so many unstressed vowels, and this likely occurred through various means depending on the nature of the syllabic violation in question. Metathesis might be one possible tactic for languages undergoing these reductions but in this particular example and knowing what we know of PIE, **mekr- isn't any better than **mker- since we find neither sorts of verbs in PIE at all. If we take our cues from Middle Chinese however, we might expect that the offending onset element was simply deleted. So perhaps we should expect **makéra- to become **ker-, not **mker-, after Syncope. One might also suspect that some phonemes were altered to fit better with sonority hierarchy. Perhaps for example, odd resulting clusters like **ml- might have been fortified to *pl- or *bʰl-. As you can now see, my previously-mentioned suspicion that *mad- 'to be drunk' goes back to maxéd̰a- by way of the vocalization and loss of laryngeal in the onset is implicated in my elaborate network of interconnected thoughts and wasn't just some whim I had at the spur of the moment. (That is, regardless of whether this word is connected to a Proto-Semitic passive participle, I really do suspect that this word once had a laryngeal in the onset because of the root's vocalism.) IEists need to ponder on these riddles more but so far either extremist conservatism or extremist whim are the soups-du-jour. I try to walk the path of balance through this age of bipolar extremisms and I hope that my readers do too.
At any rate, one thing is for certain: Syncope directly implies that a lot more went on than just vowel deletion. So if anyone is searching for a thesis topic, this is an itch just waiting to be scratched.
 I prefer to be more precise than this and reconstruct *kaxʷánasa (nom.)/*kaxʷanása (gen.) in MIE. The reasons for this however are largely beyond the scope of Mid IE and in part related to the rule of Laryngeal Vocalization in late Mid IE which I haven't yet talked about. It suffices for now to observe that PIE's initial consonant clusters are caused by Syncope and placement of stress accent.
 I must admit that this particular idea might perhaps be a hasty suggestion considering *mleuh₂- "to speak". At any rate, as you can see, there are many ways in which a language may try to normalize words that violate its syllabicity rules.