system
Given the following post, respond as if you're commenting on Reddit:
human
[Rogue 1/SW] If Scarif base could send out hundreds of Tie Fighters when under attack, why did the Death Star only send out 12 when it was under attack?
gpt
The Rebel attack on Scarif was intentionally made to look like a larger assault than it actually was. In addition, the Rebel fleet was larger when it attacked at Scarif. So basically, the Imperials thought they were getting screwed in a massive surprise ambush and sent out all they had, lest they react too little too late.

At the Death Star, the Rebels attacked with a fleet that was already depleted from the previous battles, against an Imperial force that was already in a prepared posture. 

As a rule of thumb, you only want to commit as much resources into an action as are required. Over committing can expose you to needly spending resources, or getting those resources caught in a trap.

So well prepared, and confident in their abilities, the Imperial only sent out what fighters were needed. Perhaps they were even hoping the Rebel fleet would surrender after the destruction of Yavin. Capturing lots of prisoners and ships would be a magnificent bonus to proving the might of the Death Star.