I doubled up when I was a student, and thanks to the AP exam started college with the second year of calculus. This enabled me to start taking more advanced mathematics courses sooner in college, and was very helpful to me.
OTOH, I strongly feel that students who do not expect to pass out of first year calculus should not take calculus in high school. The only purpose that serves is to make them bored in college calculus, where they often do badly because they've slept through important concepts they didn't learn in high school. They also often lack the skills in algebra, geometry and trigonometry that are necessary in calculus.
(I often remind students that calculus is actually easy. What makes students think it's hard is that they're unable to easily do the algebra that's necessary.)