Most of my 30+ years of nymphing has been without an indicator aswell. Depth does not dictate whether I will use an indicator. How far the cast is, and how many conflicting currents my fly line will be crossing to get to the holding area does. The biggest problem that i have noticed with beginners, and veteran nymph fishers alike is, most become fixated on their bobber. Yes, it's a bobber, and I use it aswell. Warren you mentioned watching your line when not using an indicator. I submit that you still watch your line even if you have an indicator on. The indicator is normally placed on the heavyest part of the leader. The butt section. I have yet to see where the line runs directly under the indicator. Normally it juts out in the direction of the nymph (s). that little section of line is what I watch when ever possible. Barring 40 to 50 foot casts in heavy water, thats practically 99% of the time. In my opinion, and thats all it is an opinion, if I am relying on an indicator to move, I feel I have probably been missing 75% of my strikes. By missing I mean not even realizing that the fish was on my fly at all. I have taught a few people to nymph fish over the years. The easyest for me to teach were a couple bass fishermen from Kansas. After an hour or so I told them think of it as hooking a bass on a plastic worm , but the bass will only take the worm as its dropping. A light turned on over their heads and they did pretty darn good the rest of the day. Once they started concentrating on line movement where it enters the water, they did well.
With or without an indicator, it will pay divedends to learn both methods, and know when to apply one method over the other.