From what I have seen, Seismic Toss doesn't seem to have been used much. All I can think of is Chansey/Blissey, and Mega Kangaskhan. Are there any more serious uses for this move besides these two?
This applies for any of OU or BSS starting in gen 6
Other then Mega Kang and the pink blobs, Seismic Toss sees use on Registeel, in conjunction with Toxic and Stealth Rock, to speed up the enemy's death. However, this is in RU.
Registeel's gen 7 RU analysis, because the gen 8 UU analyses haven't been made yet