What are the pros and cons of the concept of "1 site - 1 user" in ISPManager?

Question

System administration

Recently, developed sites have been hacked more often.
I suggest not focusing on the reasons for hacking.
5-10 sites per user (ISPManager)
And because of one hacked site, as a rule, everyone suffers.
I want to solve this problem, and at the root.
Thus, only one question is of interest:
What are the pros and cons of the concept of "1 site - 1 user" in ISPManager?
Namely:

1. Will the use of this concept affect the load on the server (percent, RAM)?
   
2. Is it true that attackers, having hacked into one site, most likely will not be able to get to another? (I believe that attackers are usually the so-called script kiddies)
   
3. Are there any other pros or cons
   

Can this concept become a "rule of good manners"?

Answer 1

I think that's why your sites break on WP. Yes, make 1 site 1 user, I have been doing this for a long time. It does not affect the load in any way. The probability that hacking one will get to the rest is minimal. If sites are rarely updated, just disable FTP and SSH for them