On glass bows, maybe not so much tillering as design. Some bowyers adjust the taper rate of lams, riser length, power wedges and tip wedges to get maximum efficiency at the desired draw length. Others don't.
Depending on the design, with average bows that are being drawn 26" - 29", a bow that is designed well at 28" works good. You could spend a lot of time maximizing it for a 26" draw for a very small gain.
The real answer is probably a little different for each design and each bowyers approach.