kern.ipc.shm_allow_removed

[Luke Dean]

The latest version of Opera claims to be faster by taking advantage of 
"shared X memory" if I set the sysctl kern.ipc.shm_allow_removed.

I don't like to change sysctls from their default settings unless I 
understand the consequences.  I've been unable to find a manpage that 
describes this setting.  The description "Enable/Disable attachment to 
attached segments marked for removal" sounds a bit frightening to me.

Would anyone care to comment on the effects and risks of changing this 
setting on a private desktop machine?