If heat is an concern, you'd probably want to spec a thicker gauge wire.

Regardless of wire gauge, bundles of wire noticably reduce your heat dissipation ability and therefore reduce your safe current carrying capacity accordingly. That's why electrical code significantly de-rates the current capacity of circuits which run more than just a few conductors in a single conduit or through the same hole.

Yes, but (especially when Cu and Al are pricy) being able to use a thinner gauge can be a big benefit.