Like, if I said "Brand ABC's watches are ugly", it sounds pretty harsh. That's how I read it.
If I were to say 'Brand ABC's watches are ugly IMO", it sounds harsh but more in a subdued tone of voice.
I like adding "IMO" sometimes to my written opinions because I don't want to come across as my opinion is the absolute correct opinion. I add the IMO to soften the forcefulness of my opinion.
It's not about of course what you're writing is your opinion so why even write IMO or IMHO - but it's how you protray your opinion in the virtual medium.
Cheers,
Anthony