Procedures and settings are really greatly dependent on the environment you have. The latter referring to security risks and requirements rarther than software.
Generally speaking there is always a trade off between how much you scan and the impact on the network, users, backups and so forth.
If the weekly scans have no great impact on your infrastructure, I cannot see any reason to change things.
While it does not hurt to scan your servers, in most situations, there is no absolute need to do so provided you have up to date AV software in place on servers..
In an outbreak situation it would of course be wise to run full scans on all systems.