I constantly use I think etc. in model-sharing mode because certainty can be poisonous both to your own knowledge and that of who you're talking to. In pure information conveying mode I think X and X are identical but it's so rare that you can know BOTH of you are in that mode that it feels way more comfortable to hedge.

Examples: What's bob's phone number? It's 555-1421!

Where is your car? it's in the driveway

Where is bob? I THINK he's at work.

What temperature does water boil at? I'm pretty sure it's 212f.

Why are people often disingenuous? I think it's because our brains view conversation differently than our culture does.

Why am I giving examples? Because I think there is a continuum, not just two modes. If you can stay conscious of it, placing yourself wholeheartedly in one mode or the other can be very effective, but it's easiest to maintain a middle ground.