While recovering data I see a warning related to recovery to the same drive. Why it is not recommended?

This can result in data on this or other (deleted) files being corrupted!!!

Why do you need to Undelete to the same drive the file was deleted from? Is this is your only drive? We try to discourage recovering to the same drive, although it is permitted. This can result in data on this or other (deleted) files being corrupted!!! 

Always recover your data to another drive first if possible and then transfer it over to the original drive after verifying it has been recovered successfully.