If I use the word "customary", it is not very often. It seems to be a somewhat dated or more formal word that I don't hear very often these days or even think of using . I'm probably more likely to use "typical", or "usual", or "conventional", or to say, "it is common practice to...", or "commonly", or, "it is traditional for...".
But, if I am specifically talking about cultural or religious customs, I might use the word "customary", because it would be more accurate in that context than simply saying "typical" or "usual". Societal and religious customs generally carry some pressure toward conformity by all members of a group. So, some behaviors aren't just "typical" or "usual", they are also expected
by a group from all members, and using the word "customary" helps to capture that sense of a group norm. For instance, it isn't just "typical" that people stand when the national anthem is played, it's "customary" that they stand.