I'm familiar with various methods of tracking disk I/O, both as a rate (e.g. bytes/second) and cumulatively (e.g. bytes) for read and write operations, however I don't know of (and cannot find) any means of tracking the amount of disk space freed by a process. I suspect this may have something to do with the complexities of defining when/how disk space is "freed".
rm file doesn't overwrite the contents of the file with some form of "nothing", but instead clears pointers and the like. In other words, it basically deallocates the disk space associated with
file. But there are many other ways that disk space can be freed up. For a pre-existing non-empty
echo '' >file clears its contents. Hard links and files that're opened by multiple processes potentially further complicate tracking disk usage since the definition of when/how the space is freed has some degree of ambiguity.