How is that a small (semi invisible) application can drain your battery and slow your computer

Screen_Shot_2017-04-11_at_2_54_33_PM.png

I never thought that Magnet, an application to snap windows from one place to another would raise the CPU usage from 0 to ~80% every time I switch from app to app. I guess this thin makes some sort of computing every time I do that switch.

Loading