Garrard was re-signed earlier this month and was placed on the exempt list. Garrard previously retired after a stint with the Jets over the summer.
If all goes to plan, Garrard will probably never need to play, but he gives the Jets another option in the event of a Geno Smith injury. When Garrard cut ties with the Jets before the season, he said it was because his knees couldn't cope with practicing every day so he couldn't back himself to win a quarterback competition. However, if they're able to manage his reps as they have done with Kellen Winslow and others, then he should be able to remain available.
While Garrard hasn't played in an NFL game since 2010, he did play in preseason in 2011 and I broke down the film here.