^ Time is the universal measure (and for some the ultimate goal), but it's also VERY general; it tells you you're improving (or not), but not HOW to improve. And as others have also noted, knowledge of your time and that you're being timed has its price in terms of distraction, decision-making, and possibly insurance coverage.
I would argue that at the beginning and intermediate stages when you're still improving by leaps and bounds before you start working harder for smaller improvements in advanced groups, you don't need a timer or telemetry to tell that you're getting significantly faster; it's just too big a difference not to be perfectly obvious. Your instructor will be able to tell you what general techniques you need to work on or start incorporating in order to continue going faster. Telemetry comes in AFTER you can consistently and correctly apply all of the general techniques and want to see the impact of minor line/technique adaptations.
I'm out there to become a skilled driver and of course have a great time. Smoothness and technique application IS actually my end goal, not lower times, because I see fast lap times as a byproduct of achieving my goal. But striving for fast lap times won't automatically make someone smooth or skilled in technique. You get fast by being smooth, not the other way around.