Servo5 vs Mot_PWM - how they differ?

I posted this question several times under single copter category (that’s my drone), but very few people goes there so I have not received any answer. Perhaps I will have more luck here. Here’s the question:

Servo5_Max and Mot_PWM_Max - how they differ since both control the same motor assigned to Servo5 (option 37 selected)?

For clarification - I have a gasoline engine powered single copter. The throttle servo for the engine is assigned to servo-5 output.
However changing Servo5_Min or Max seem not to affect anything while Mot_PWM_Mix/Max does limit the range of that servo.
The firmware is 4.0.5
It’s really important for me to understand the difference.