Is there a rationale behind it, or do you just feel that way? I have never run into issues with this, and real coding bugs like the one in GOG Galaxy, where play time =time_process_end - time_process_start instead of continously sending heartbeats like steam, are probably a bigger issue.

I think I fear system instability and its consequent (probable) problems.

Sleep does a lot of things, a lot I don't necessarily understand, all the OS layers are stressed at once, and with them a whole lot of other things, bith software and hardware related. Are all the drivers of your system trustworthy, are all the running applications trustworthy ? Are we sure no data loss will occur ? Will you lose audio, wifi, display or excessive battery because of a race condition or an error of some sort in an element of the whole involved stack ?

Most of the time everything is fine, or is it ? Maybe your computer will hit kernel panic after two hours or so, and you will have hard time figuring the real cause and origin.

tldr; I think it scares me because it increase the probability for the system to surprise crash at a very crucial time (while compiling something, in between two saves of a text buffer, during a write to disk...)