Newbie ? - what is the dressage whip for in lower level?

Can be used for many things: impulsion, leg yield, just a simple reminder to stay focused (I'm a beginner in dressage BTW ). I know it's used for higher level dressage elements (my trainer mentioned it when we were discussing on how to use one), but I don't have real knowledge on that.

Actually I almost never change sides either. My horses are stiff on left, but much more relaxed on right (plus my right side is stronger). So basically I rarely need to re-enforce the right side, so my whip mostly stays in my left hand. During lesson my trainer rarely asks me to switch it aslo. Only if horse is reluctant to go in certain direction or ignores my leg completely.

BTW some people simply ride with 2 whips. I never tried it but should be fun.

I've experienced the opposite: I was dutifully changing sides when finally my instructor (a judge and very experienced, originally from Germany) finally got frustrated and told me to stop changing sides!!!! She said it was very disruptive-- difficult to change the whip and keep a steady contact, for anyone, and that it was much better to use it on the side you need it, and leave it there. It didn't occur to me to ask if you needed it on both sides. I imagine she'd have suggested using two, as already mentioned.

And that is why I prefer to ride with two whips ;)

Your instructor probably just wants you to learn how to use it properly. It's your choice whether to use it during a test. I use it to re-enforce my leg, but have only actually used it while warming up, so far not during a test.

Actually yeah, my response was for using one during the ring work. As for test I sometime used it to reinforce my leg on walk/free walk (she doesn't have enough impulsion).

As has been pointed out by others, horses often have a stiffer side. I use the whip to back up my leg. I am usually able to do what I need with my leg but, it is there in case. I use it to energize and this can be done on either side. If I need it for lateral movement it will usually be on the "stiff" side, which is where the whip will be. On a rare occasion I might have to switch.

I almost never carry two whips. It ties up both hands and I always prefer to have one free for whatever else may crop up.

Two whips become excellent ''defenders'' when warming up before a competition.

If by "defenders" you mean hitting people incroaching on "your" space in the warmup ring, I would suggest it takes two people who are not paying attention to cause a crash. I hope this is tongue in cheek..funny talk.

Riding stallions in a warmup is something we have both done. We accept a greater responsibility in the warmup as a result of our deciding to show stallions. And, yes, it CAN be a real nightmare!

I forgot to answer the BIGGEST reason I don't switch sides. The connection between rider and horse is a very delicate thing. I don't like anything that interrupts this connection. Switching sides with the whip is absolutely going to offer such a disruption that the connection will fail. No way to do it well enough for the horse not to get distracted by it.