Depends on the map, but if it's some large repetitive and irregular shaped one like a NES platformer then yes, lots. Also, some tile map editors support exporting the map in that format.
So if you want to uncompress a line of 48 chars from 3x3 tiles that's 16 tiles which may be all or partially the same, and if the tiles are stored so you can look up the char data from row 0,1,2 then it's pretty efficient.
Cheers,
Simon