Hi Bri. S.
The benefits of Class Mode is that it forces you to do some faster poses. This is to get you comfortable with doing "gesture" drawings which are usually drawn quickly to focus on capturing the overall pose of the figure.
Some examples of "gesture drawing":
https://one1more2time3.files.wordpress.com/2008/10/gest3233.jpg
http://3.bp.blogspot.com/_m0Dbm9A6jM4/S7iNaGJwBEI/AAAAAAAAAEc/5SYWTSioqzc/s1600/sketchbook_040310_01.jpg
This can be very beneficial as it can loosen up your arm and also warm you up. If it helps I think of it like a bodybuilder lifting some heavy weights. They will usually try to warm up their body by doing stretches (30sec-1min pose) and then once they're warmed up they do their heavy lift (5min-10min pose).
The other benefit of doing quick poses is that with practice you'll find your line quality will become more confident. This is because you generally have to place your lines quickly and thus you become more decisive about how you move your pencil.
I would encourage giving it a try with the goal of being able to capture the WHOLE body/pose in a relatively quick amount of time. At first it'll be challenging and you'll likely have a hard time getting it all in 30seconds but in the long run it can be hugely beneficial to your drawing.
Hope this helps! Cheers!
- DK
