Well caus i don't use lot fo characters at same time i never noticed that ... Pro only ...
hummm ... hummm ... a so basic technic that exists from lot of years ... i prefer to shut up ...

Yep for paths , you should calculate them every 5 , 10 frames or more ... like people using navmesh, you don't callfunctions each frame.
It won't be noticeable at all and it's not some racing game or Fast paced FPS game also ...