I think the primary objective in any DE (or probably any track event) is to bring the car back in the same shape that it arrived in.
Second is to learn the line and to be smooth.
Third is to learn to drive (and brake) comfortably at high speed.
Eventually, you want to combine all of this stuff to drive quicker and quicker lap times.
I think DSC is appropriate all the way through the first 3 objectives, but you need to be aware of what DSC is doing for you and when it is doing it.
I started with DSC on and drove 4-5 HPDE's before I decided to turn it off. I spun twice on the first session with it turned off. I am lucky I wasn't sent home. My mistake was that I didn't pay enough attention to when DSC was intervening. I developed some bad habits obviously. I braked when I wanted even if it was in the middle of the turn. I was also on the gas much too aggressively out of turns. DSC was doing a lot of intervention, but I wasn't connecting my driving with the feedback it was trying to give me.
Long story short, leave it on, but pay close attention to when it intervenes and why. For the most part, you should be able to get around the track pretty quick without it intervening at all. When you do that, chances are you're smooth enough to drive without it.
If you have MDM, that's probably the best way to go as it intervenes a lot less and you'll learn the limits much quicker (in relative safety).
At some point, you'll not like the intervention and will want to take it off. Unfortunately, there is no real good way except for seat time and perhaps drifting practice to learn how to recover quickly enough from a significant oversteer event - you'll want to make sure you're anticipating where it can occur and be ready rather than trying to randomly react. I am not thinking that sliding is faster anyway, but as you get faster you will occasionally cross the line and you need to have the reflexes and skill to react.