To clarify, in all liklihood - you would be doing top tier on spot, and then 2nd and third via other methods... but there are ways to get a system to really handle spot loss...
There are MANY applications that simply are too complex to handle such an arch... so, - do so, when you can, but know when that's just stupid.... stacks are like snowflakes, we LOVE them to death, or we love them to DEATH...