|Yes, that's a useful trick. The 0 is treated as a delimiter, and CMD.EXE seems to remove all leading delimiters (but not trailing ones). It's just the same as how you usually do your for /f loops:|
for /f "tokens=* delims= " %%a in (....)
When you use this, for example, to list the contents of a file, you will notice that it modifies all lines that begin with spaces. Judago's trick is the same, except it uses 0 instead of space.