Well, there's at least one use for them: some machines I've used have had a terrabyte-long /var/log/lastlog file, due to uid -1 being inserted in it, or something like that. It would've been a shame if that actually took a terrabyte of disk space (although that's actually feasible now!). :)
Of course, on the problems side, this caused havoc with RPM, since under some conditions I don't really understand, it would try to read and checksum the entire file, every time you tried to install a package. But hey, just need to teach RPM about SEEK_HOLE, and it'll be all great!