I did a brief stint into online dating - I met someone whom I saw for just over a month. I added him around week two, since I wanted to get a look at his FB page. I would not add someone before we had gone on at least two or three dates.
I think it allows people a kind of neutral space to explore each other a little; what someone's posting or has posted in the past can be very illuminating as to how they are as a person, especially when you're still on the 'best behaviour stage'. Things were going well in person, and I was able to browse around his page and his pictures and see that overall he seemed to be a genuinely nice guy who didn't have loads of drunken photos, or super political posts, or anything like that. I don't think it's a lazy way to get to know someone at all, since presumably you're still talking on the phone and having dates with the person. It just allows you to see another side of them.
In the end, it didn't work out. The day before I told him I didn't think we should keep dating I blocked him from seeing my FB posts, and a few days later I quietly defriended him. No muss and no fuss.