Stadia is going to eat data faster than a hungry dog eats dinner. This might not be a big problem for a lot of Europeans, as most data providers on the continent provide affordable uncapped data plans. However, this is not the case in North America, which makes up a lot of Google’s customer base. For Google to make its money back and thrive in the competitive gaming market, it has to succeed in its home market. With data limits being strict and with expensive penalties, gamers may choose to steer clear of the service to avoid unwanted bills at the end of the month.
And the biggest disadvantage is you require internet - a good connection in fact.