It all depends on your network architecture and how you have your clients access the services. It's not all cloud, of course.
Possibly the most important reasons for subnetting:
Geographic separation: You separate geographically remote location into different subnets as routing over long distance (WAN) manages and scales better than bridging.
That's sloppy writing in the instructions, but I'm pretty sure it means you should use /24 networks (i.e. 172.16.0.0/24, 172.16.1.0/24, 172.16.2.0/24, etc). It would've been better to say to use class-C-sized networks, but even that's obsolete terminology since network classes haven't been a thing since 1993.
By the way, 18.104.22.168/.123 are no private IP addresses. You should never use public addresses that you're not authorized to. Check out RFC 1918.
There are two basic approaches:
You configure a separate network (p2p, switch, VLAN) for each machine and connect one server NIC to each network (but both within the 22.214.171.124/21 subnet or larger - which ...