Maintenance of what little hand-eye coordination I have is why I play video games. Social contact with nice people in MMOs is the other. Voice commands and well thought out macros are a godsend — I still play Perfect World (on a private server) and despite my boundless spasticity I’m still one of the more sought after clerics (healer) for dungeon runs
Crescenda, via forums.mmorpg.com

One of my buddies from the Marines wants to play ESO the only problem is he lost a good bit of mobility in his hands from an IED in Iraq. Would there be a way for him to macro his attack combinations so that he could actually play the game or do you think he would be banned for it?
jstans_ESO, via forums.elderscrollsonline.com

Games that involve a large amount of repetitive sequences of actions can result in pain and fatigue, in turn resulting in reduced play sessions.

Macro functionality, i.e. being able to set up complex sequences of actions that can then be executed by a single click or keypress, can provide a hugely beneficial relief from this, significantly reducing the demands that interacting with the game puts on the player.

External automation tools exist, but use of these is usually a bannable offence under EULA/TOS. Providing the functionality in-game is a way around this, providing a means of automation that is under full control of the developers.

Best practice example: World of Warcraft
Best practice example: Final Fantasy XIV