It includes pointers to updated packages and descriptions of each vulnerability. If no steps are taken to fix known problems then the system is still vulnerable. Often, administrators will read new vendor advisories, but then get distracted performing other tasks. The system then sits idle and remains vulnerable until a new release of the distribution is installed. The process repeats itself.
Advisories are often numerous and annoying.
This is why it is necessary to have the minimum amount of packages installed. It should be your sole purpose in life to make sure that vulnerable packages are patched as soon as an advisory is released. Advisories dating back to June 2000 provided fixes to today's Ramen worm problem. If not this time, it will be the next. Staying current is extremely important.