You want to have as little waste as you can. You also may want matching pieces. IE. Nose and butt sleeve from the same piece. As you cut the piece down you can also get point stock from it if the dimensions are right.
ok, i'll be the oddball
i like 48" plus
30" for full length butterflies and leaves me minimum 18" for standard cues
preferably 8/4 , also giving me extra pieces to use as veneer
and as dave sutton said, no waste, it all gets used one way or another
more in line with OP's question though ,
24" for matching fronts and buttsleeves (that arent really sleeves on my cues)