I hunt public land only and choose to harvest "mature" bucks and bulls or I will purposely harvest a doe and cow for the meat. My motivation for letting immature bucks/bulls walk is two-fold. I am not gonna b.s. anyone,I love matching wits with big mature bucks or bulls and I do like quailty racks in relation to my area. Second and not least important by any means, I care about the over all health of the herd. Killing the young bucks/bulls and not harvesting does/cows accomplishes nothing. Infact, it weakens the quality of the herd in many ways and decreases opportunities for future good hunting.
As far as putting a 125 inch minimum on what you shoot and what you let pass... I believe that "size standard" are relative to the area your hunting. For example, a 125 buck in Florida would most likely be a mature deer and a quality one at that. (Heck a 125 buck with bow is good anywhere!

But in other regions a 125 inch buck could possibly be a young buck....say 21/2 or 31/2 years old. Depending on what you consider mature. For me I try to hunt 41/2 year old bucks, but often have harvested 31/2 year old bucks. My reasoning for setting a standard at 4 1/2 is that most bucks skull plates reach full growth in their 4th year. I am fortunate to hunt public ground that offers a good age structure, not high in deer density but good over all age distrubution.
IHW,
Shed