yes, now drive around a tight corner with some bumps in it. Then do it faster. Just because it doesn't hit the fender stopped with the wheels straight ahead doesn't mean they fit
Also, a stock 1g wheel weighs 22 lbs. most good aftermarket ones are between 15-18 lbs for 17" You can get used RX-7 wheels(FD) that weight 13lbs each.
I forget the exact math on this, but one lbs at the outside of that large circle is equal to about 5 lbs on board the car. Or more, I may be wrong. It also kills your ride quality due to huge unsprung weight. If the energy the bump is putting into your suspension cannot move the wheel easily, it will move the whole car instead. But thats only one side effect.
See, your engine has to work against not only the larger lever arm of that 19" wheel and tire combination, but it has to turn all that extra weight ON that long lever arm. You know when you get a real tight lug nut on your car? What do you do, you get a big ass pipe and put it on the end of your wrench. This gives you more leverage. And if you still can't get it off, you jump on it. Why? To put more weight on that lever. Your 19" wheels are working against you with those same 2 principles. Only they are doing it on all 4 wheels. Now if you take the difference in wheel and tire combos and express it as lbs/feet(mass on the end of a distance gives you force, usually expressed as torque). Yes, this is written simply, not as a formula or in engineering terms, but simply to be understood.
Now, this is not just bad for forward acceleration(and it will slow you down for sure) but it will kill your braking, your handling and your fuel economy too. Braking because your brakes have to fight that large lever to stop the slowing down of that rotating mass. Handling because the geometry of your suspension is all out of whack and because the extra mass on the end of it is much harder to move than the spring and shock rates are setup for. And mileage because your engine has to work that much harder to get it all up to speed. Its worse than if you just tossed the big wheels and tires inside the car. Much worse.
But you can say that you got 19" wheels to fit in your 1g wheel wells and I didn't