I personally never boot the raq after the install of a new pkg even if the cobalt wants it.
This is what sun has to say about it.

Cobalt Server Uptime

I change configurations fairly often with my Windows NT server, and this requires restarting. How often do I have to restart my Cobalt server?

Based on Unix, the Cobalt servers are designed to run for months at a time. Most services and add on software do not require you to restart the machine.

About the only time you must restart the server is if you change the IP address.