Phone Taken Away

I've never actually done this or been through this situation but I know people who have and I get why.
Tbh I hate when my parents did it to me.
If it's your partner I dont think there should be anything to hide neither should you put hide contents mode on your WhatsApp.
As I see it, it allows a partner to have a piece of mind in a way but shouldnt be overly excessive like every day looking in each others phones.
I see many people find out their partner is cheating by doing this so at least they dont have to waste long on a meaningless relationship.