Whether or not to sandbox

Well, I'm considering building apis in ways that allow easy sandboxing of programs, or not.
The thing is, I see many OS's which do so, and it has to have some cost, e.g. for protecting calls to getfenv you need to keep a blacklist of environments, or keep important OS variables local and pass them around. I.e., it's probably possible but an headache for devellopers.
Thing is, sandboxing that goes beyond maintaining an API self-contained/blocking access to running code(e.g. running programs, the Lua interpreter) and goes all the way to sanboxing programs run by users seems useless given it's complexity and the fact that computers are cheap.
But perhaps I'm missing something?

Must people want to sandbox something to show they have the skill. They do realize computers only take stone/gold, redstone and glass to make, but ComputerCraft is about what you create with Lua, not what you make with stone.

MechaTallon, on 16 December 2012 - 10:09 AM said:

snip

Sandboxing is about letting other people run programs in your computer, without letting them interfer with your stuff, whether it is just protecting files or programs running in the background.
That said, that was quite poetic. +1