I can relate a moment I had when I was first getting to know Cubase.
it has a 'warp the timeline to the music' feature. the tutorial I found for 'time warp' or whatever was to show how to determine what the BPMs are from a piece of audio. It used some Pretenders track. Find the downbeat and drag a barline to it, find the next downbeat, et cetera.
what was discovered in this process was this 'rock solid' beat wound up being a number of BPMs, in fact. Conforming the beats to what was played showed there was breathing room not only bar to bar but beat to beat.
when I make something, I don't quantize the music. I quantize the timeline to fit the music after I have the time like I like it.
I made a couple pictures for you. This is a reggae-styled track.
First is the tempo track as a list, then some piano roll with the clav. part [highlighted], which was the basis for a scratch track for the rhythm guitarist before I had him do his bit:


I could have further warped the tempo track to fit everything inside the bar but it's close enough for rock 'n roll. Since I didn't do that, you can see how the backbeat, 2 and 4, at times hit behind the tempo a smidge.