I don't see an issue saving them as favorites. That is what it was designed for.
For TV Series keep in mind that if your service provider changes servers on and series_id in the back end or shuffles things around, your favorites may show the program and imdb/tvdb summary of the show, but may not show the different seasons and episodes available (if the series_id has changed). If this happens, you would need to remove that TV show from favorites and then search for it, and add it back. It happens from time to time.
For LiveTV channels, I have way over 200 favorites and I even have 2 favorites categories (one for me, and one for the boss herself). For TV Shows, I typically have a dozen or so favorites which are the ones I am following typically. For Movies, I typically add them to my favorites when browsing, to tag them "to watch". But once I finish watching them, I untag them.
But I don't see any issue adding them to favorites. Sure the B5 is the entry level basic series 5 box, and relatively slower than the more expensive boxes, but it won't harm to add favorites. That is one of the basic features, may as well us it.