Autopilot use during approach

I've moved up to a new plane that includes an S-Tec 50 autopilot. It has
several very capable modes ranging from Wings Leveler, Track a Heading bug,
Follow NAV input, Hold a set Altitude, and approach mode which tracks NAV
input more closely.

What do the regs say about the permissible use of an autopilot after the
enroute portion of a flight that is being conducted under instrument flight
rules? To what extent is it permissible to use the autopilot during an
approach? For example, after the controller says "radar vectors for..."
through DH?

Thanks!