[plt-scheme] Why box here?

There is a call to a text% editor get-filename:

file:///C:/Program%20Files/PLT/doc/mred/mred-Z-H-677.html#node_tag_Temp_678

You can pass in a box to get the result or you can just get the result
from the function itself.

In the DrScheme code calls to get-filename do both.

collects\framework\private\frame.ss line 1148.

In my code, I just use the result of the function.

http://planet.plt-scheme.org/package-source/grettke/drsync.plt/2/1/drsync.ss

Both seem to work fine.

Why would you use either way or both do check the result?