Chalking or soapstoning a file keeps "pins" from embedding themselves in the files grooves, between its cutting edges.
This prevents gouges being dug in the workpiece, thusly, a better finish.
Keep your files clean, wrap them in cardboard, rag, or whatever to keep them from being beaten up whilst in the tool box.
Also, keep the file FREE of oil. Oil makes the file "slide" on the workpiece, instead of cutting cleanly. (Degrease your b/heads befroe filing on them.)
A quality file will give years of good service if it is looked after, so buy the best you can find. (Grobet, Nicholson) They are not really expensive.