[gentoo-user] best practice for kernel mainteneance

[Thanasis]

Regarding kernel maintenance, mostly from the point of view of security, 
which is the best way to go:
1) Having gentoo-sources in /var/lib/portage/world, which would mean the 
sources would be upgraded whenever portage marks a newer version as 
stable (provided someone follows stable)?
2) Not having gentoo-sources in /var/lib/portage/world, which would mean 
the sources would be upgraded only as a dependency for some other 
package (which is quite improbable/rare)?

(or, I may be missing something :-) )