DOS 3.3: BSAVEing a High Resolution Screen Economically

Since the starting address and length of a binary file are stored as the first four bytes of the file, saving a file with a length of $2000 actually stores $2004 bytes and therefore requires one more sector than $2000 bytes would.

You can avoid using that extra sector when you save a High-Res screen by saving it with a length of $1FF8 instead of $2000.