Anything ST covers first gets sent to them for assessment. They do minor stuff, but if anything major is needed, they sent to the manufacturer's authorized shop for repair. This is where it can get frustrating. While ST guarantees a two day solution, it does not extend to outside repair, so you are at the mercy of Nikon, say, who took three months to fix my body the first time and several weeks on each of its other trips in. ST did mollify me with a $50 B&H gift card each time, so they recognize the issue. All things considered, the coverage was worth every cent -- I am getting a new body after 2 years and 275,000+ clicks.
If you go for it, make sure to get the pro plan with free shipping and 100% "whatever happens" coverage.