Now I understand what is happening. It’s the cursor position.
I didn’t know that position of the cursor is also very important during the snapping. Well, I guess you’ve mentioned that in the tutorial but I’ve probably missed that part.
I was trying to snap the chair to the floor, and as I said before, that was working perfect in perspective view because from that view I could see a big part of the floor. But, once I’ve switched to side view, since the floor was very thin line, Blender wasn’t able to “understand” that I want chair legs to snap to the floor however close I’ve put them. In fact, what I have to do is not to position chair legs to the floor but the cursor.
Thanks for helping! 🙂
