PlayerControler Init with PIE mode and SIE mode

I find that when i use a GameMode which is override the default playercontroler with my own playercontroler, if start as SIE mode,my own controler was not create but a default PlayerControler was create,even i hit F8 to switch to gameplay mode,i still don’t get my own playercontroler.
But if i started as PIE mode,my own PlayerControler was created,even i switch to SIE mode,my own playercontrol is still exist.
Is there any different between start as PIE and start as SIE? Or is some special design in this situation?