Adjustable Rockers

[azfrc]

When do you need adjustable rockers versus non-adjustable rockers.

[Firebirdjones]

I prefer an adjustable drivetrain myself. It becomes mandatory with a solid cam of course. I also prefer a full roller rocker so switching an LS motor over just makes more sense to me anyway.
Some like the simplicity of torquing down the rocker shaft assembly. Nothing wrong with that, you just have to have the appropriate length pushrods to establish correct preload on the hydraulic lifters while at the same time keeping correct valvetrain geometry.