Best way to use Network Discovery

We have a 500 license for both NPM and NTA. This will cover all our switches, routers and wireless access points over 19 subnets.

Obviously there are lots of other devices on the network that we don't need to monitor.

What is the best way to scan?

A full scan of each subnet and select what we need?

Within each subnet we have allocated a range of IPs for PCs and printers. Do a scan of just the ranges within each subnet we need?

Just wondering what is the best and quickest way to scan when you don't want to monitor everything.

Thanks

Nathan