I'll share what I wrote in reply to @braaiboy comment on the same matter.
For visibility, good comments may be upvoted just enough to get them seen. Upvoting all comments is a bit too much to justify in my opinion.
That's my opinion. Some people are strictly against such a thing and some are supportive of voting every comment if they wish to.
Yeah I guess it's a case by case basis and some Steemians are ok with it. I completely understand the need to do it if you are trying to make a point and add some value to the convo....But completely understand the annoyance of upvoting things like 'Great post' lol