It heavily depends on the gameplay for me. The more specialized classes and jobs are,
the more immersion and role-playing is involved.
Sadly, a lot of RPGs come to a certain point where it is totally unimportant as what you started as almost anyone can do the same more or less.
Looking at MMORPGs, I guess the most visible reason for this is the balancing,
but it also happens in single-player games quite often.
So to put it short, the more specialised the character/class is,
the better (and more fun) it is to role-play for me.
the more immersion and role-playing is involved.
Sadly, a lot of RPGs come to a certain point where it is totally unimportant as what you started as almost anyone can do the same more or less.
Looking at MMORPGs, I guess the most visible reason for this is the balancing,
but it also happens in single-player games quite often.
So to put it short, the more specialised the character/class is,
the better (and more fun) it is to role-play for me.