I pretty much stay in 4WD all the time when I'm in the woods or fields with my Ford 2120. On the New Holland TN75, I sometimes flip in and out since it's only a switch on the dashboard. The TN also has a switch to lock the differentials which automatically unlock it is on longer needed. On the 2120 since it is kinda a pain to go in and out of 4WD, I probably could run in 2WD a fair amount, I just don't bother. I do know that anytime I get stuck, it's when I'm not in 4WD.
Andy