If there's one constant in hunting, it's unpredictability. One thing that's predictable though is that you won't encouter many bench rests out in the woods. If you practice these three shooting positions in the off-season, you'll be prepared for a variety of situations you may face in the field that don't allow you to get prone.
Standing with a rest is useful when tall grass, brush, or other obstacles would obscure your sight in a lower position. You can use whatever trees or rocks are nearby to create stability and a comfortable shooting rest.
Seated with a front end support like your hunting pack or tripod can offer a really stable position that utilizes a tool you'll have with you on most every hunt. Spend some time with your gear figuring out how to make this comfy and tolerable.
Last, a kneeling position is mandatory knowledge for making quick, accurate shots. You can do this with a front end support, but you can also get great support just by locking your elbow to your knee.
So, go shoot. Then shoot some more and try some different positions while you're at it.
