When you read a post or news item, you may n't have time to check what the author is saying, or whether you got anything out of it...not all the time.
Hence it's time filler? May be sadly! hence it's necessary to check once in a while, and to spare a few minutes & think how our study is of any value!
If you understand that author's viewpoint, it's good, no matter whether you relate to it or not!
If you grasped author's viewpoint, and you identified you own viewpoint - whether it's differing with authors, or in line with author's to whatever degree, perhaps it's better & absolutely proper thing to do - you made the most of your time spent to read.
In our busy lives, it's not uncommon for people to read through a lot of things, without understanding a thing. But unless you do it properly, it's nothing but time-passing, and nothing more indeed.
The best way to check whether you are doing right thing, esp when you are reading online, is to comment on what you read. When you express, you express yourself - and it helps you!