Basic NIOS can do basic Network Discover:

Data Management > IPAM > Select network and click “Discovery”. IPv4 only and uses NMAP.

The NetworkInsight license (a.k.a Discovery license) allows the Infoblox to use SNMP and other protocols to discover and catalogue a diverse assortment of device types including routers, enterprise switches, firewalls and security appliance, load balancer, enterprise printer, wireless access points, end hosts, application servers, etc.

So, NetworkInsight provides better data. However, as with the built in discovery functionality, you need to be careful. Depending on how and where it is being used in the network, it may be advisable to deploy more appliances (e.g. one in America, one in EMEA, one in APAC, etc) to reduce the amount of probing traffic flowing around the globe.

WHen deploying multiple devices, you use NIOS devices for probing the networks (we call them probes) and they report to the “consolidator” devices which then report to the Grid Master. Technically it can happen on the Grid Master (or preferably the Grid Master Candidate) but that can cause messness with the firewall rules.

A NetworkInsight appliance can be standalone. It can't do DNS or DHCP but it can gather IPAM data just like a “normal” NIOS Grid.