When do floors and ceilings matter while solving recurrences?

Question

I came across places where floors and ceilings are neglected while solving recurrences.

Example from CLRS (chapter 4, pg.83) where floor is neglected:

Here (pg.2, exercise 4.1–1) is an example where ceiling is ignored:

In fact in CLRS (pg.88) its mentioned that:

"Floors and ceilings usually do not matter when solving recurrences"

My questions:

1. Here does "usually" means ALL cases ? If yes, i can just forget them all the time.
2. If not, then when do floors and ceilings really count while solving recurrences ?

Note: This ain't a homework problem. I thought about it while I was refreshing my DS and algo concepts.