I played through a crusade where free summoning was allowed and it became pretty degenerate really quickly.
3 Characters started summoning hordes of poxwalkers, greater demons and other characters that on the next turn, could summon as well.
Its a unfun mechanic and unless the narrative calls for it, I think reinforcement points should be enforced imo.
That way both sides are on a even footing. Its a bummer that the mechanic is so poorly thought out but the Chaos player isn't gimped from having their forces accounted for when mustering their forces.