Unprivileged user?

[Ricardo Newbery]

I'm trying to understand the purpose of the "-u user" option for  
varnishd.  It appears that even when starting up as root, and the  
child process dropping to "nobody", Varnish is still saving and  
serving from cache even though "nobody" doesn't have read/write access  
to the storage file owned by root.

I'm guessing this is happening because Varnish is reading and writing  
to memory instead of the file storage?  So I suppose my question is  
what functionality is missing if the effective user doesn't have read/ 
write privileges to the file storage?  Is the backing file only  
accessed by the parent process?  And if so, what is the purpose of the  
"-u user" option?

Ric