and "Server owners" will be available to server owners when they create new domains. To allow use of this template by domain owners (i.e. Server owners) you must enable at least one other server type).
I don't understand what's "server owner" option in server templates.
What's its features? -if I deselect it what don't I have on virtualhosts that use this template?-
a server-owner is a domain owner
or your client that bought a hosting package from you.
When you enable a template for a server-owner then your client can make use of this template when he creates a new domain. like a subserver or toplevel domain etc.
This is useful if you create a template for sub servers which you want your clients to use instead of the default subserver template.
You can think of other ways to use it.