So, Diablo has two "realms" in which characters can be in, the seasonal realm being one of these. As the name suggests, the seasonal realm is where seasonal characters play through seasons, which are periods of time in which players attempt to complete multiple levels of increasingly difficult challenges. Playing the seasons can earn a player rewards, both free and paid, through the battle pass, which unlocks these rewards based partly on seasonal progress. Seasonal characters are created new at the beginning of the season, and transfer to the other realm, eternal, at season end, where they persist.

Being that there are paid rewards, I can understand and support Blizzard's reaction. Allowing players to exploit a paid service, even in a way that seemingly doesn't effect others, sets a poor precident. Beyond that, I'm not sure if there are ways in which it effects me, but I've not participated in much PVP, which I think would be the most obvious advantage, as otherwise we're not competing.