There are two sorts. For some unknown reason some of those looted by the player early on have higher than normal stats (equivalent to normal runes) but are titled "lesser". These cannot be combined. Others have lower stats for the lesser rune/glyph, and combining 2 gives a normal rune/glyph, which again combine in 2s to give a Greater Rune/Glyph.
I've been throwing the first sort onto my equipment and then discarding when selling obsolescent gear, while the second sort I've been slowly crafting up, and am recovering if needed by dismantling gear if I need the rune/glyph for new equipment. (mostly I'm just making new as I need them as they are found like candy, as with most other "rare" or "unique" loot).