How can I save part of a file to a new file in vi?

Sometimes it's nice to be able to pull out a piece of code or text from a file and save it to a new file.  Maybe you just need lines 48-105 of a file and want to easiyl extract that. 

In vi, you can do the following while editing the file:

:48,105w smallerfile.txt

this will save the lines 48-105 to the "smallerfile.txt"