Reduce CPU usage.
You do realize that SLEEP isn't the only command which limits CPU usage, right?
DO
a$ = INPUT$(1) <-- this drops CPU usage to almost nothing as well, while waiting for a single key press
Or, just as simple:
DO
a$ = INKEY$
_LIMIT 30
LOOP UNTIL a$ = whatever$
SLEEP is honestly a problematic way to go about this type of process, as it's basically nothing more than a DO: _DELAY 0.01: LOOP UNTIL _KEYHIT type process, and there's some old versions of QB64 where SLEEP breaks with unwanted out-of-focus keyhits. (Such as SHIFT-TAB which should be OS reserved to switch app focus between programs.)
INPUT$(1) works much better for a hard pause, while _LIMIT or _DELAY is better with INKEY$ or _KEYHIT, if you make use of ON TIMER events.
(At least, in my opinion...)