actually, building it into the cam adds more stress than adding it to the rockers. when you build it into the cam, you accelerate all the valvetrain. the lifters, pushrods, rockers, and valves.

by changing the rocker ratio, you only accelerate the valves. and you end up using less seat pressure for the springs due to the leverage gain from the rockers. building it into the cam is just a less expensive way of doing it. and that's why you need more seat pressure on the springs. they are having to control the entire movement of the valvetrain. not just the valves.

do a search for mark campbell and quiet tahoe. they have made numerous posts regarding this matter.

 

downside? none really. most will try to tell you that you're limited in cam selection by going to higher ratio rocekrs. again, i'll refer to the graphs i posted where vinci tested that theory. smaller cam made more overall useable power than the larger cam. you pick the right parts, you get the right results.
here's the CHP article with the 5.3L truck.
www.stealthram.com/reddogplan.htm

here's my gain from the wife's car using stock cam.

dyno 9 before
dyno 11 500 miles later
dyno 14 10 months later
all on stock tune