What's the deal with -boundscheck?

[Walter Bright via Digitalmars-d]

On 4/5/2015 10:15 PM, Walter Bright wrote:
> A new switch was added, -boundscheck=[on|safeonly|off]. It
> took me a while to find it at:
>
> http://dlang.org/dmd-linux.html
>
> because whoever added it didn't realize that the list was alphabetized and stuck
> it in there after -map.

https://github.com/D-Programming-Language/dlang.org/pull/960