In the system settings (based on this article http://docs.prospect365.com/en/articles/2860832-preventing-users-editing-quote-records-in-certain-statuses) you are able to set whether records are editable in different quote statuses and can set whether they're editable by everyone or just Admin users.
However, it may be the case that you might want to edit just one field on a confirmed quote/order but leave the others read-only so it would be useful to be able to override this setting on a field-by-field basis.