Essential
In my view the DRS, hot spot and snicko should all be used in every form of the game. It's incredibly frustrating when your team loses because of a poor decision or two. It's also unsatisfying when your team wins because of poor decisions. The technology is available and should be used all the time. There are huge amounts of money in cricket these days, so the cost of equipment should not be a consideration.
Also, having just 2 reviews in the DRS is not enough. EVERY decision MUST be correct. I know there is the time wasting issue but teams could be punished in other ways - fines for slow over rates etc. Also, umpires who regularly have their decisions overturned should be sent back to school.
I'm not having a go at the umpires, they have an INCREDIBLY difficult job, but even more reason to use the available technology!