IF you have a large MATV system, you amp the signal first.
If that signal was sent to a TV, it would overmodulate, causing interferance.
Amping would be nessesary due to the long cable runs and multiple outlets.
The further you go, the more signal loss you will have.
The aim is to have a good signal, of say 65db on all outlets.
After the Distribution Amp (the DA), the signal might be about 95DB
Taps will drop about 2db across them (from in to out) & attenuate the signal on the tap acording to it's specs.
In the case of this example, the first tap would need to be 30db to drop the signal to 65db
At the other end, after 100M of cable & various taps, you may not need to attenuate the much at all, maybe only 6db
Another reason to use taps, is because they isolate the outlet.
If someone shorts the outlet for example, it won't effect the rest of the system.
So, when planing your system, you would meter the signal, then figure out the cable loss acording to it's specs and balance the load around the system useing taps.
Does that make any scence?