Is this a serious question?
AFAIK, 2-week payroll makes for easier payroll calculations all around and stabler timeframes for most(?) processes.
Back of the napkin calculations are easier too... Weeks in year? 50 assuming 2 weeks vacation. Means 2000 hour budget for full time employee. Project gonna take 10,000 hours? You need 5 full time employees. etc etc of course some of these are just estimates but it gives you a good idea of costs.