There's one thing about led dimmers and controllers that have confused me, were planning to put in over and under cabinet lighting, with both strips on at 100% the system should be running with 72 watts total, however the RGB controllers specs say the max output can be 48 watts. Since i'm only using a single color for the bottom and only RGB at the top, the RGB strip will consume 24 watts, the problem is, if the entire system takes a total of 72 watts, but the top RGB set only takes 24 watts, would anything happen if I used a 48 watt dimmer to control the RGB strip which takes 24 watts in a 72 watt total system? Does it mean 48 watts only on the RGB side or does it matter how much is also going in? I plan on sharing one power supply rated at 12v 7a for this system, where i will split the paths for the upper and under cabinet strips.
The RGB controller's output is only relevant to the 3-color LED section. Per 60 LEDs, they use 0.4A per channel (1.2A total). 48 watts is 4 amps.
So if your strip is less than 10 feet long you should be within limit of that controller.
If you are near or exceed the limits of that controller, you can add a device called an amplifier in between the controller and the LEDs. The same controller can power several amplifiers if needed. At that point, the controller's output is no longer used for power, but merely as a signal to the amplifiers. So if the signal has some distance to go, it can travel on thin thermostat cable instead of heavy cable.
You will not be able to use the RGB controller to dim the monochrome strips. It will not do what a person expects, unless they know a lot about RGB blending, which your guests won't.
Also keep in mind these cheapie LED dimmers are not intended for use as on/off switches, and will leave components energized even in the "full off" position. Not something you want to do. Aside from being a fire risk, it will be a considerable vampire load 24x7, which will drive up your energy costs.
The better way to think of dimming is as a fine adjustment after the switch.