First is the case in New York some years back. They "regulated" bitcoin businesses by requiring them to sign up for a license that had a lot of restrictions and high taxes. Not only it didn't facilitate mass adoption, it did the opposite by forcing business out of NY.
Second case is in Japan where they accepted bitcoin as a legitimate currency and also removed all taxes from payments made in bitcoin. That helped the bitcoin adoption speed up since businesses were more comfortable to accept bitcoin.
It didn't change anything in adoption of cryptocurrencies aka altcoins though.
As you can see regulation on its own is not good or bad. We have to see this as a case by case basis to figure what kind of effects it is going to have on the bitcoin adoption.