It can be used where ">" does not work, e.g. when using sudo. So you can do echo data | sudo sponge /etc/a.file `tee` can be abused in a similar way, but it

It can be used where ">" does not work, e.g. when using sudo. So you can do echo data | sudo sponge /etc/a.file `tee` can be abused in a similar way, but it also prints the data to stdout, which is ugly.