Their purpose is to fully test all of the technology being used in the performance (lighting, sound, automation, special effects (e.g. pyrotechnics), etc.)
Usually it consists of the lights being cued in sequential order, fixing any problems along the way such as brightness, angle, framing, or position.
Lastly, for stage shows, the fly rigs or battens are tested for weight and accuracy of cueing with sound and lights.
If there are moving set pieces, the crew will test their operation and mechanics (if they are automated) and practice their movement, flow, and position on and offstage.
There may be an extra step for particularly effect-intensive productions, such as film, TV, or Broadway-style stage shows, where the crew tests any special effects that require systems such as rain, fire, or explosions.
If the show is on tour, additional tech rehearsals may be held to cover issues that might arise from being in a different size/shape performance space.
Paper Tech is a rehearsal without sets or actors, used to allow the technical and design team to discuss aspects of the show.
Stage managers use this rehearsal session to ensure everything is written correctly, all cues are in order, and the crew is prepared for the show.
[4] In the amusement and theme park industry, dark rides featuring special effects based on various technology have occasionally been operated in early phases described as technical rehearsals.