1-piece cranks use 1/2" spindled pedals
3-piece cranks use 9/16" spindled pedals.
When you go to buy your pedals there is almost ALWAYS the choice of getting them in 1/2" or 9/16". So, I guess that is another advantage of 3-piece cranks... They use a pedal with a larger spindle that won't break as easily as the pedals on 1-piece cranks.