Gunuts it depends,

If you were going to Hunt and carry the bullets in you pocket Crimping is a good idea.  In Cast Bullet assocation matches the general rule is bullets have to be seated in the case secure enough to carry without the bullets dislodging.  Also if your powder is slow and needs to be helped to get up to intended burning rate a crimp can be the way to go.

However if accucary is your aim and none of the above apply there is nothing about crimping that will help, As a rule the less you do to your bullet the more accurate it will be

Boats