There are various factors why you would want to drop comprehensive - the most obvious are what the replacement value would be if you totalled your car.
For me, I drop collision as soon as the replacement value is less than $10,000 - no matter how much it costs. That is a much higher threshold than many, and is typically a little more than 12 times what you would pay annually as a premium. I drop compreshensive soon after, or usually at the same time.
My reasons are as follows:
1. I really hate paying insurance.
2. I have only had one accident, when I was 16 years old, and have not had a claim that was my fault since then ... over 35 years. (note "not my fault")
3. If you are a good driver, and never had a claim, or seldom have a claim, your threshold should be higher. Note that if it is someone elses fault in an accident, the OTHER driver will pay to have your car repaired - so comprehensive/collision insurance is only if the fault is yours.
4. Are you in love with the car? If you really don't care if the car is totalled, or damaged and drivable, then again, your threshold will be higher.
You pretty much have to be your own actuary and determine if it is cost effective to drop insurance for your specifics. e.g. for most people if they NEVER had to pay insurance for their entire lives, they would be ahead of the game. For others, they get some value from their insurance, and get more than they pay into the system. The latter group is less common - the majority of us pay more into insurance than they get back, and that is why insurance companies exist - to make money. You pretty much pay for collision to "insure" against that one time catastrophic loss amount.