I have mowed 5 acres of law for 26 years with my Deere 955 compact util and 72" midmount. I have a lot of hills but the only time I engage the front axle while mowing is when cutting along the roadside ditches where the bank is pretty steep.
There are plenty of times I engage the front axle when using the loader and sometimes I also use the differential lock.
I have a Kubota F2690 on order which has auto 4WD to take over the finish mowing duties from the Deere 955, it will be interesting to see how often it engages 4WD while mowing.
When turning, the front and rear axles are tracking at different angles and tire slippage at one or more wheel positions has to happen with a 4WD system that doesn't have a differential as part of the transfer case. If all of the tires have good traction, then a lot of force is being generated. Worse with this type of 4WD system is when either wear or inflation causes the design rotation speed between front and rear to be off spec even when going in a straight line.
Any driven parts wear and that wear happens even in normal use. But when it is under much higher stress which is what occurs with 4WD when all wheels have good traction, then the wear rate is much higher.
VE9AA, how long had you owned your tractor when you noticed the warm front axle? Differential gear sets develop heat in normal operation but this heat generation is much higher during the first hour or so of operation even at the low speed of tractors. With new cars, the biggest beneficiary of a proper new vehicle break-in is the differential assembly which can generate extreme heat during initial operation. With my RWD vehicles, I do an initial rear axle fluid change at 1,000 miles knowing that there are going to be considerable wear particles generated during the first few hundred miles of operation.
Rodger