Quite often there can be a bit of a dip in the torque curve as the HP starts to get it
its act together (and it can sometimes have a bit of a dip or flat spot too). The
theory of the crossovers is to adjust the tuning so that it minimizes the flats spots/dips
that can occur in the middle RPM ranges. Different engine designs behave differently,and
the other factors like how restrictive the mufflers are, among other things, also play a part.
You may not notice much difference. In theory, the top end of the RPM range may benefit
slightly from removing them, but I bet that it wouldn't be very noticeable on these airheads.