automatically set processor affinity mask not checked

I take that by default for multi CPU machines, the "Automatically set
processor affinity mask for all processors" is checked in the properties of
the server in SQL 2005
My question is, if its not checked, what does that mean and what are the
pros and cons of it ?
So how can I check which processors are being used ?
If I look at the processors, all the processors are checked ?
So in essence, is it the same thing as if this setting was checked ?
"Tibor Karaszi" <tibor_please.no.email_karaszi@.hotmail.nomail.com> wrote in
message news:A1C1FE69-965D-4A38-B1B8-D61E5CB38CD0@.microsoft.com...
> Check out sp_configure and the "affinity mask" option. Checking the
> checkbox means 0 (all processors can be used). Un.checking this box is
> setting it to some other bitmask, where you specify which processors can
> be used.
> --
> Tibor Karaszi, SQL Server MVP
> http://www.karaszi.com/sqlserver/default.asp
> http://sqlblog.com/blogs/tibor_karaszi
>
> "Hassan" <hassan@.test.com> wrote in message
> news:OPwvm$7VIHA.2304@.TK2MSFTNGP06.phx.gbl...
>