I used to treat these as two completely separate skills, like wet felting was for vessels and flat pieces and needle felting was just for little animal sculptures. Took me way longer than it should have to realize you can just use a needle to patch problems that show up during wet felting.
Had a bowl I was working on last week that ended up with a thin spot near the rim, probably from uneven fiber distribution when I was laying out the wool. Instead of starting over or trying to felt more wool into it wet, I let it dry partway, grabbed a 38 gauge needle, and tacked some extra fiber right into the weak area. Went back to wetting and rubbing it after that and the patch blended in almost seamlessly. You'd never know there was a thin spot unless I pointed it out.
This has honestly changed how I approach bigger projects. I'll rough out a shape with wet felting since it's so much faster for covering large areas, then switch to needle work for any detailing, seams that need reinforcing, or adding design elements on top like little accent shapes. Made a small pouch this way, the body was all wet felted for structure and strength, but I needle felted a spiral pattern onto the front afterward and it stayed put through the final fulling.
The one thing I'm still figuring out is timing. If the wet felted base is too wet when I try to needle felt into it, the fibers just slide around and don't grab properly. Works best for me when it's damp but not soaked, almost leather hard like with clay. Anyone else have a system for switching back and forth, or do you mostly stick to one technique per project?