"I think" also marks a reflection on the state of mind without any implied uncertainty. That is, it implies that the thought originates from your own mind, rather than from some deferred authority. As in "I think we should do X" in opposition to "we should do X" where I've just walked into a meeting after getting off the phone with my boss. I don't want anyone to get the impression that I'm merely relaying orders.

>Removing it would change the statement to one of fact or make it prescriptive when it may be better taken as descriptive or a possibility among many.

There are better ways to make these distinctions, and in most contexts, you don't need to differentiate between facts and opinions on account of the difference being obvious. And where it isn't obvious, it's obviously debatable, and people will do that regardless of whether you make such a qualification.