This might be a giant hole in my reserves knowledge base, but my understanding is that SELRES/traditional reservist loses Tricare eligibility from the time they retire, until age 60. I know Army reserves/AF reserves are pretty different, in terms of active retirements, but is this not the case for us?
Regular 20 folks get the medical and pension payments right away. Reserve Retired can use the stuff @snake020 talked about after they retired until 60 (gray area). After 60* you get the same medical as the folks who retired with 20 active. For myself and many others, it opens up the possibility of retiring between 60 and 65 from airlines instead of waiting it out till 65**. I fly with a lot of 60+ year olds and many lament the cost of healthcare before Medicare as their reason for not retiring early.
* 60 minus any time on Title 10 orders, so if you did any MOBs, a little early. For me it'll be 59 and 4 months.
** I'm going to assume anyone hired at a major in their 30s, put anything into TSP, and didn't give half of it away to their first wife can make the math work to walk at 60, or at least go to an L/Dmax type schedule.