I have this and it is excellent.
The idea is that no matter what else collects ice, you will have power. This is obviously important. Depending on the aircraft, it can take a LOT of ice before you lose significant lift but it will take very little ice on the prop to seriously clobber the ability to climb, especially if you are already at say FL100+.
You need power to climb, and climbing is one of the escape routes (depending on what the TAT happens to be; if it was say -2C and there is 5000ft of safe air below then I obviously wouldn't climb). If you get serious prop imbalance (due to ice) then you may have to reduce power and you are stuffed; the only way is down.
As for despatch capability, and known ice certification, the whole subject of what constitutes "known ice" (particularly in the UK where "icing in cloud" appears on every F215) has the potential for a very long thread indeed....
The general idea with flight into potential icing is that you must always have an escape route. A deiced prop gives you more options in that department.