This phrase seems like a powerful phrase to me. Say someone states their opinion on something like, say, Minecraft. They just say "minecraft sucks". When they say this, it gives others the impression that the one saying this believes that their opinion is definite and that starts arguments and disagreements. If someone were to say "in my opinion, minecraft sucks" or "minecraft sucks IMO" it wouldn't give the above stated impression. I feel that if people were to use the phrase "in my opinion" before or after stating their opinion things might be more peaceful with less arguments?
I mean, that's just how I feel, others may feel different. Just wanted to express my thoughts.