With either feature, a headrest is usually necessary for the times when you are tipped back. When you are in a reclined position with either of these features, the physical forces on your vertebrae are reduced since your weight is no longer pressing vertically down on your spine. Pressure on the sit bones is reduced considerably. The weight of your body is being transferred to the back of the chair. Less of your weight is transferred to your seat, so pressures change across the skin surfaces in contact with the cushion.
Circulation is helped.
And it is just a plain relief to have a change in position. In some cases, both tilt and recline features might be incorporated into the chair. Using tilt first helps maintain posture, but some additional reclining relative to the seat might still be necessary to accomplish sufficient pressure relief. Your therapist will be able to determine if you need a combination of tilt and recline. If you require a fixed recline angle that you use at all times, select a chair with a back that can be set to your exact needs, but would rarely need to be changed.