First, and the less obvious of the two, is
the abundance of ammo.
Not exact matches
This isn't like your standard shooter where you can find clips
of ammo in
abundance; it's easy to become a miser with regards to bullets as you never can tell what unfathomable scenario you could find yourself in next.
During most boss fights
ammo can be found laying around in
abundance, but I did encounter one situation where I simply ran out
of ammo during a boss fight and there was none being spawned.