Looking at the earlier comments, that code was merged-in in ab997b8, hard to see the original context though since that is not a merge commit (just a regular commit).
It does mention this thread, most of which is obsolete. There shouldn't be anything special about recording-vs-playback, however I would put a couple of caveats on there:
most REAPER APIs are designed only to be used from the main (GUI) thread, not from audio threads or from plug-in-created threads.
pretty much anything done during playback should be able to be done during recording. If you're modifying track recording parameters, those parameters may not latch during recording until recording is stopped/started again (or the track disarmed/armed, etc).
from the main thread, if you set state, you might be able to interrupt audio, but in general it shouldn't be a crash.
I don't really know what the original intent was, I'd try testing a lot with that check disabled... but it shouldn't be necessary in general.