If you are reading the text of a person who presumably care about that person state of mind and what this person believes. If you don't why do you read the text in the first place?
I do think there a difference between someone thinking an event is unlikely with p=0.2, p=0.01 or p=0.0001. It worthwhile to put a number on the belief to communicate the likelihood.
If people frequently provide likelihoods you can also aggregate the data.
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.