As been mentioned a bit - 'need' is a funny word.  
Years ago my mom was looking for a pick-up to haul a trailer. While shopping she mentioned she wanted a 2wd. When I asked why she is not looking at 4wd trucks she said "We will never use it. It would be a waste. We don't need it."
Fast forward - they never bought a trailer yet the truck gets stuck on almost every 'lets go cut down our own xmas tree!' adventure and when it snows a lot, they take (and risk) their sedan. Also - they do NOT buy winter or traction tires,so that's huge....but the point is about 4wd or most anything, you will not need it until you need it, then you will be glad. There is no downside to a front locker if you can afford it. Frankly, i'd consider a front locker before a rear locker maybe. 
Also look into the 2wd low range modules. I have one enroute for my tacoma, and when I pick up a locker for the rear end I may never 'need' 4wd. But when I do, I surely will. 
