Hi!
The question sounds like: why we need water? Yes, some orders works without flags (like MOVE in '51) but some of them cannot work properly without flags. Take a look at 80C51 family programmer's guide available in the net. Some of orders are modifing the flags (like SUBB) and some of orders are using modified flags (like JZ after SUBB).
By the way : do you know that MOV in ST62 family is changing some flags (like Z)?

Greetings,
Jacek