[erlang-questions] BIFs use with care

[nato]

I recently saw an ESL video advising that one should
use Erlang BIFs with care... it was a bit of an aside, so
I was wondering if someone could could elaborate
on this. It seemed to suggest that BIFs (the ones written
in C?) could block/cause problems ...

After many books, this is the first I've heard of it and would
love a rundown on things to watch out for regarding BIFs.