You're definitely not crazy for asking!
There's actually an online tool your oncologist can show you where you enter the specifics of your diagnosis and then each possible treatment. A bar graph goes up by varying amounts and you can ascertain the survival percentage with each treatment.
As the others have said, it's mopping up. It works for many, but not all, and there's no way of knowing which group you'll fall into. My mother had chemo in 1986 and is still here. My sister had it but it didn't work for her and she died two years later. I've had it and am crossing my fingers.
It's a decision only you can make. I'm like @kezmusc, I don't want to have an 'if only' moment and so have thrown the kitchen sink at my cancer. Whatever you decide just be sure you're comfortable with it. K xox