In plumbing, there are the following types of connections (that I can think of right now): compression - uses a ring and a tapered seat to press items together; washer, straight on compression (like in a garden hose to the valve), tapered threaded connection - mechanical fit, but leaks around the threads if you don't seal it, and flared fitting, where the end is flared out and pressed against a specially shaped end (also compression). So, most rely on compression of some sorts - it could be metal to metal, metal to rubber (washer) or interference fit (like in the taperd pipe threads with sealant between).
Between the faucet stem and the outer housing, it uses packing material, which sort of act like a washer - tighening the nut compresses the material around the stem to create the seal.
To assess whether pipe dope or teflon tape is required, you need to understand what type of seal is trying to be made. Tape or sealant are designed to fill the gaps on tapered pipe threads. Every other type of fitting relies on a different method to create the seal, so adding anything to it can potentially compromise operations - get in the way and make it so it can't seal. Pipe dope or tape can act like a bandage, but may not ultimately, produce a long-term solution. Basically, unless it is a tapered pipe thread making an interference fit, no, you should not use them - they get in the way, and can make a perfectly good joint leak.