I know it's not a practice exclusive to the metal genre, but it's the genre I listen to predominantly so I notice it more in metal.
Personally I think it's a thing that should be done more often. I know it can come off as lazy, especially if the band/artist hasn't really progressed, but for the ones that do it gives a clear illustration on how a band has evolved. I've noticed some of my favorite bands doing this (not that it's a recent trend) but if often gives me a new perspective and a better appreciation of the music, especially the older styles.
My favorite example is probably "All Alone" by The Sins of Thy Beloved - I prefer their EP version because of softer vocal style, but the album version sounds drastically different (especially around the 3:20 mark in both versions); it's a much more refined sound
Your thoughts? Favorite re-recordings/re-releases?