Main advantage is redundancy on pitch control. Lose and aileron or rudder servo - no big deal, lose the elevator and then you get to try to fly the airplane with the throttle and/or flaps for pitch control (but probabably not for long). This being said, I opted for the less redundant single servo mainly because I didn't want to split the elevator shaft and install a second hinge point (like on the Beaver- page2 -post 28). I was toying with the idea of placing 2 servos in the stab itself but would have had to use mini servos, but I didn't think they would be up to the job.
I plan on doing through preflights on the control systems and also the Eagletree inflight Telemery system will signal if the electrical system starts drawing too much current ( main battery current sensor along with main battery voltage sensor and receiver voltage sensor {after the voltage regulator}). I have the same system on my 1/3 scale Ventus 2ax and it provides "piece of mind" while flying ( 25lbs of Sailplane )