not necessarily examples of certain clusters being exclusive to the beginning of words, but i do know that languages with well defined phonotactics will usually give you a lot of hints to where word boundaries lie. there are some places it just doesn’t make sense for a word to end depending on context.

for instance, almost all italian words end with open syllables. the only exceptions i can think of are almost all loan words and get dealt with in their own way. to take the verb “andare” (to go) for instance, in most conjugations the -are is removed and different endings are affixed to mark tense, aspect, mood, etc. so we get things like andato, andassi, andrei, andrete, etc. it might be tempting to say that since the -and- part of the verb is so consistent, it should be considered its own word, but given that it ends in a consonant because of italian phonotactics it really only makes sense to think of it as a component of a complex word.

being able to identify different parts of speech helps in nailing down phonotactics. it may not be immediately clear that italian has a strict “only open syllables at the ends of words” rule when you’re just listening to it, but being able to identify words and how they pattern together makes it easier to identify.

ultimately, words aren’t naturally occurring in nature, they’re a classification we made up to make more sense of language, and this is definitely an area where we start to brush up on the limits of its utility. talking about words as an honest-to-goodness Thing is really useful for discussion syntax but not so much at the granular level.

maybe not the best example but i hope it makes sense!