I'm cutting a hole in an internal wall to install an enclosure ready for fiber install.

There is a wooden batten nailed to the stud and then the dwang is nailed up against that leaving a gap. 

It is the same at the other end of the dwang against the adjacent stud however the dwang above is normal and is flush against the studs.

Whats the reason for doing that that? Is it just to allow cables to be put in later and if so can I expect to find it everywhere? 

It's a 1950s brick house if that makes a difference.