This isn't generally regarded as necessary for a TAS to be valid, but it allows it to work on TASBot and similar rigs, which can help it get in front of a wider audience. It also helps figure out which TAS techniques are theoretically possible in non-TAS runs.
http://tasvideos.org/TASBot.html
In addition to TASBot, there's also a growing practice of using physical rigs to "verify" tool-assisted runs:
http://tasvideos.org/ConsoleVerificationGuide.html
This isn't generally regarded as necessary for a TAS to be valid, but it allows it to work on TASBot and similar rigs, which can help it get in front of a wider audience. It also helps figure out which TAS techniques are theoretically possible in non-TAS runs.