if one considers the increase in resistance to deflection or torsion for a singular tube in isolation, then the net effect would be insignificant... however almost the entire frame structure is affected in a compact/sloping frame design. the incremental increases in resistance to deflection of each shortened tube becomes accumulative and compounded when assembled as a structure. not only are the toptube and seatube shorter & stiffer but the seatstays as well. virtually every attachment/bracing angle becomes more acute and the structure as a whole becomes squater,and more efficiently triangulated .