In TV listings, the term "repeat" means the episode was shown on TV before, but it doesn't mean we've all seen it.
When I program a series to record repeats, it's often because I missed those episodes. Once I watch those repeats I usually don't want to them to be recorded again once I've erased them. Some of the more popular shows (i.e.. "Big Bang Theory," "Law & Order," "Seinfeld," etc.) have repeats on many days on many channels, often doubled by HD and standard versions of the same channel.
The way things work now, allowing repeats to be recorded often means having to constantly erase what I've already erased, sometimes the same week or even the same day! Pain in the neck.
If there could be a way to mark particular episodes as something like "do not record again" or similar, I can still look forward to the repeats I haven't seen without having to deal with the ones I have.
Perhaps the system could (if it doesn't already) work in a manner where it knows, automatically or manually, what's been watched previously. This way, an option can be created in the series programming to choose whether or not to record episodes previously viewed.