The other is ensuring the stick exceed the min_check, max_check thresholds so stick commands work.
Another explanation be joshua bardwell: Max and min channel values are determined by the rxrange command. Max_check and min_check are used to decide if you are entering a stick command.
If it is then this indicates that there is not enough processing time to complete all the features that have been enabled.
On newer versions on the ßF Configurator the CPU loading is displayed in the Status bar and MUST be less then 100%, preferably less than 50%.
More recently Boris decided that he could possibly make improvements on the way the PID control loop works and forked an Experimental version as Beta Flight.
Therefore documentation on ßF and CF tends to only show what is new or changed and the documentation of previous Firmware must be read.
So there is a dead space at the bottom of the throttle range (below min_check) but no dead space at the top of any channel range.