If you want to keep your extruded surfaces as clean as possible, you can also first extrude the individual curves, then merge the surfaces into a single surface (yes, a surface, not a polysurface) with the “Smooth=No” option. This way, you can simplify the geometry, especially when you have to deal with intersecting surfaces or polysurfaces for Bolean operations or fillet edges.
The following is a very good example showing where that technique solves a problem that occur with surfaces that were joined instead of merged.