Not useless, but it can go bad much quicker. A few years ago I lost a rotary hoe because the engine had been damaged and the carburetor had gotten clogged. The fuel was less than a year old, but closer in color to cooking oil.

If gasoline sits in open air or a non-sealed container for a long time, its lighter fractions will eventually evaporate. The heavier fractions can cause blockages and misfires. It can still be used, but you have to dilute it with fresh gasoline. If it happens while inside an engine, the carburetor should be rinsed with fresh gasoline to remove clogs.