Well that depends on how the bow is tillered. You should be able to get a bow that is twice your drawlength. The major reason for sinew when I do it is to add poundage and drawlength to a stave. There are very few people that will admit that they don't draw their drawlength on every shot.
If you are making a bow for someone else or making a bow that you will let anybody shoot, then tiller it out to max drawlength. I hunt with my bows so they may be drawn to any given length. I would like to hear others thoughts on this though.