You don’t have to use modes if you have everything working The way you want without them. 
Modes are most useful, I think, when you want to have a single device act in two different ways.
For example, at sunset we put our house into “night” mode. At that point, if you walk past the motion detector in the bedroom, it will turn on the overhead light. During the day, walking past the motion detector will not turn on the light. And when I go to sleep, I change The mode to “asleep.” At that point, walking past the motion detector does not turn on the overhead ceiling light–But it will turn on a soft night light on the wall.
So here we have the same room, and the people doing the same thing, but different results depending on the mode that is set.
The following topic gives some other examples of how people use modes. But again, if you don’t need them you don’t have to use them.