Deciding whether to go SB....

I have used SB before and one of the biggest drawbacks is lack of coverage..Like the Detroit fly in, I can see because of the extra coverage.Can someone clarify how people use SB when not all of the flight plan is covered at certain times, or perhaps has never had coverage?For example.I depart Denver with VATSIM controllers, then when I fly out of their range, then what?? If the next Center is not covered, what do you do next? Then it is kind of hit and miss with coverage at the destination. So how do SB users fly?Do you switch over to FS ATC? Do you let the FMC fly with no ATC? What is the point???Please enlighten me..I see quite a few flight sim pilots flying on VATSIM, my question is with the lack of coverage, how and why if the ATC process will have gaps of coverage? This is not very realistic.. So why is VATSIM / SB so popular?Thanks!Barry