The only time I’ve actually used this feature is on the hardcore server toward the end of the season.
I bought a few shards to reroll low levels chests (feywild and toee, did a stick build). Then after I had all the achievements I wanted, I’d log in once a day for a cheaper gold rolls until I depleted all the leftover shards (20% discount!). Shards won’t transfer, but those XP stones and other goodies do.