This feature was introduced in Version 13.
When an object is checked out it is locked to the PC. No other PC can modify it. When it is checked out read-only, it is not locked to the PC. So it is important to check out read-only if you don't intend to modify it.
There is an unlock option in the Visual LANSA Editor if you need to allow another developer to access it.
It can also be unlocked on the IBM i.
Change Task for an Object in the LANSA for i User Guide