Let's say I have to use the 192.168.X.X address space for numerous sites.
I would like to correspond the 3rd octet to the site but still separate different traffic for the site - maybe separate for 4-5 different teams/departments. I don't want things to get out of flow or have problems let's say if these sites began to expand or double in size.
Does let's say using /28, then /26, etc. subnets sound like the best approach if I must use 192.168?
It all depends on the machines you have in each department and chances of expansion. I would recommend using 192.168.x.x/23 for the bigger site and 192.168.x.x/24 for smaller sites. Then equally divide the subnet further department wise.
For example, use 192.168.0.0/23 and you have four departments at this site then divide the subnet as follow:
I think 126 usable IP's are enough for each department.