combine legion and Consul

[l'canadien]

what's the advantage and cost to combine one legion with one general

[Jim-NC]

If you have multiple generals in the stack, the extra generals (not the 1st on the left) can be attached to units. They provide a benefit to fighting (IIRC +1% per offensive or defensive point of the general). The main leader provides a bigger bonus to the whole stack if not attached to a specific unit.

I am not sure there is a cost, unless you don't get the extra bonus for attaching the leader.