Multi-Variable Throttle Control.

[BadAstronot]

For basic launches with central liquid fuel tanks with a shuttle and solid rocket boosters, the shuttle can be quite heavy. To support the weight of the ship, you have to apply as much power to the shuttle as the main liquid engines and solid rocket boosters in order for the vehicle as a whole to be stabilized. But that's not easily accomplished as you can only control general throttle. It'd be neat to have a secondary throttle gauge or even a whole numbered panel for different throttling positions for different engines so that you can lower the throttle to the max thrust of a smaller engine and have SAS control the difference.

[vexx32]

You can adjust the Thrust Limiter setting in the engines' context menu in order to achieve this. I'm fairly sure it's available in the VAB as well as in-flight.