Unless you had a tremendous amout of power, I don't think you would normally be using attenuators if you could already dial down the power. 99% of my work is with client devices, so I'm not positive on this point.
Thinking about this topic again, I decided I would set my starting power level to, at most, one notch below maximum.
I've looked at hundreds of (client) radios and no matter how good they were, they all started to go into compression, by at least a small amount, when the power levels were raised toward the advertised maximum. To maintain signal quality I would want have the radio power levels high, but keep EVM excellent, and not have much spectral overgrowth.
The spectral overgrowth is going to increase with the higher the power setting on the radio, regardless of the amount attenuated between it and the antenna.
One of my goals has alway been to follow a "good neighbor policy" as best I can, and keeping overgrowth low is one way to do this.