It is conceivable that a site may only want ILL to be a staff function. Currently it is all or nothing, i.e. if it's enabled it appears for staff and patrons. We should add a syspref to allow it to be hidden outside the staff interface.
To make things a bit more complicated: you might have another 'thing' for adding ILL requests, like a special search interface/portal and still want to see the requests, but not options to change or add new.
As reported in bug 24806, in 19.11 (and onwards) this syspref is missing giving users no option to hide OPAC ILL request forms if a backend is installed.
*** This bug has been marked as a duplicate of bug 24806 ***