You kinda have to map out an amplifier with your radio using a peak reading wattmeter or oscilloscope and an average reading wattmeter will not tell you what you need to know. Take for example a perfectly working, stock, non modified radio should put out close to 4 watts dead key no modulation. At 100% modulation, if it will reach that, the radio will be putting out 12 watts peak. This is normal and every radio should do this, otherwise its not working properly. With AM modulation, the sidebands will add 6dB of power at 100% modulation, or an increase of 4X the power.
Now take an amplifier that's rated at 100 watts, that's all it will do no matter what you drive it with and its saturated at 100 watts. If your 4 watt radio runs it up to 100 watts or 90 watts or somewhere close to its maximum power with a dead carrier its not going to work properly when you add modulation. If the amp dead keys at 100 watts with no modulation, it will need to put out 400 watts peak when the radio is fully modulated, otherwise you get a bunch of distortion and only a fraction of the range increase that you would have if its working properly.
In this case where you have an amp that does 100 watts max and its saturated, then you would want to adjust your radio to produce about 25 watts dead carrier when the amp is on so that it will reach 100 watts under full modulation, getting the full 6dB increase when modulation is applied. I would say 90% of all amps used on CB are not used properly and dead key near full power and when you modulate it has nowhere to go but down (the toilet).
If you just want to jam people out and never talk, then by all means adjust your radio so the amp puts out full power with a dead carrier. You will cover up more people that way. If you actually want to talk you will talk further reducing your drive level so the amp will achieve that 4X increase in power when talking.
Don't be one of the dummies that doesn't know how to drive an amplifier and pick one that is appropriate for your radio and drive it with the right level. In the end you will be running much less dead carrier power than you think is right, but when you get that 4X peak power increase fully modulated the end result is the radio will sound identical with the amp on or off but the power and range will be much better with the amp on. Listen carefully to most amps out there being used wrong and when the amp goes on, the radio sounds different, it lost a lot of punch and clarity, gained a bunch of flat topping and distortion and some people think that sounds ok, but its not. Its pure trash because its owner is clueless.