In the Image

The Plumber is pulling the Tape Tight in a Clockwise Direction to force the Tape into the Grooves of the Threads.

So which is it

Thread Tape or Pipe Dope/Joint Compound?

Thread Tape or as it is often Referred to as Teflon Tape or Plumbers Tape, is made for the Purpose of Sealing Pipe Threads by filling any Gaps or Space between the Threads when attaching Fittings or Connecting Pipe.

Pipe Thread Compound or Pipe Dope is also Successfully used to seal any Gaps or Space between the Threads when attaching Fittings or Connecting Pipe.

Should you do More

Maybe, Some Plumbers suggest both to Prevent a costly Fitting or Joint Leak.

When doing both, the Tape should be applied 1st. Teflon Tape should be Wrapped (tightly) into the Threads in the same Direction that Tightens the Connection (clockwise), also cover Threads 3/4" to 1" up the Pipe.

Three to Five Wraps should be sufficient depending on the Thickness of the Tape.

2nd would be the Pipe Thread Compound or Pipe Dope. This should be applied in a way that the Material is forced into all of the Thread Grooves and cover Threads 3/4" to 1" up the Pipe.

Curing Time

Pipe Thread Tape/Teflon Tape or Plumbers Tape there no wait time or curing time.

Pipe Thread Compound or Pipe Dope also has No Curing Time if, the Line Pressure is less than 125 PSI, if the pressure is at or near 125 PSI wait 4 hours before Pressurizing.

Be Careful

Use Caution if you are threading a Male Fitting that is going inside a Plastic Female Fitting, too much Teflon Tape will increase the Diameter of the Male Threads enough to Break the Female Fitting from expansion.

Plumber's Putty

Don't Confuse Plumber's Putty with Pipe Dope/Joint Compound.

Plumber's Putty is used when you want a Compression Seal between two Surfaces. When you install a Sink Drain, Faucet, Tub Drain Plumber's Putty is the Proper Product.

“Thread Seal Tape, Teflon Tape or Pipe Thread Tape was in Part an Accident Discovery, in 1938 by a DuPont Chemist, Roy Plunkett. Polytetrafluoroethylene (PTFE) or Teflon, was the Discovery which is used to produce the Tape used by Plumbers and others.”