I think in the past, aircraft engines were relatively unreliable and would often quit midair for reasons other than fuel starvation so there'd be some chance of the other engine saving you. Now, however, almost all engine failures are the result of fuel starvation and two engines will die just as quick sans fuel as one so the added complexity isn't quite worth it, from a safety perspective for piston powered aircraft. The only real advantage now is that you get to go a faster (though not 2x) in a twin usually and get to earn lots of miles on your credit card since you'll be doubling your fuel bill.

The situation on turbine powered engines is completely different. The above only applies to piston engines.