Thinking about it, I cant really think why you would want to do steep turns in real life!
Sure, you look up and there is another aircraft filling your screen. (I have been there once as a “passenger”). The reaction is instant and having made an immediate and very rapid turn of up to 90 degrees you establish back on straight and level and thank your God he missed you. No time for HASELL or anything else for that matter.
Perhaps steep turns are there because it is a good way of establishing the student has a reasonable mastery of the aircraft and could turn away from a conflict in real life without losing control.
For this reason they are a worthwhile practice for any pilot and a very good starting place for aerobatics. Also for this reason the student should be taught good practice because he will go on to do them by himself. A HASELL check takes 30 seconds - that’s all. Before practicing steep turns why not check you are doing them at a safe height (the aircraft might just stall or spin), it is worth checking you have put the flaps away, everything is secure, the fuel is on the correct tank and you have enough to prevent starvation and just in case the engine stops you have in mind where to go, and you are not going to surprise another aircraft.
When he practices them for himself the HASELL check will be automatic and the time he has just done some slow flying, thought he would practice a couple of steep turns, and forgotten to retract the flaps he might be grateful.
Before an aero session a couple of steep clearing turns are a nice way to start. I get the HASSEL checks out of the way then - maybe old habits just die hard!
I can guarantee you one thing whether or not you were taught to do HASELL checks before stepp turns, when you really need to avoid another aircraft filling your screen the reaction will be instant!
I suppose it is a bit like an emergency stop in a car - if you are practising you might want to glance in the rear mirror before doing it!!