A constant output power transmitter will give the same output power regardless of the input level. This makes installation very quick and easy, with no requirement to adjust the system gain to achieve the correct output power. However, there are a number of other advantages:

No dependence on cable length

Self stabilising ODU with temperature

No complicated interface with the IDU

Later changes to installation, such as changing cable length, will not affect the EIRP

The benefit of a muting transmitter is to the satellite owner, or the person buying the transponder space. Imagine 100,000 transmitters all looking at the same satellite. When they are not transmitting, they are still producing noise, all going towards the satellite. This limits the maximum number of terminals pointing towards the same satellite. The Invacom transmitter shuts down between data bursts so preventing any noise being transmitted, allowing more terminals to be pointing towards the same satellite. This makes the space segment costs cheaper.

It all depends on whose transmitter you have bought. An Invacom 2W transmitter can be operated at 2W without any problems. This is because it will meet all the Eutelsat & Intelsat specifications when working at its rated power. However, when many manufacturers rate their transmitter at 2W they mean the P1dB ( the output power where the gain has compressed by 1dB) is 2W. If you were to operate the transmitter at this level, you would splatter unwanted power into adjacent satellite channels. Typically a transmitter will need to be operated around 1.5dB below it's P1dB power. The typical P1dB for an Invacom 2W transmitter is +35dBm (3W) allowing the unit to meet full specification at 2