ip - What are the implications of expanding an internal subnet mask?

Our network is currently working on a 192.168.0.x subnet, all controlled through DHCP, except for the few main servers who have hard-configured IP address settings.

What would I kill if I changed the DHCP-published subnet mask from 255.255.255.0 to 255.255.0.0?

The reason for doing this is not because we have a huge sudden influx of machines, but because I'd like to start partitioning specific devices into specific IP ranges (to be neat and tidy). For what its worth, I don' plan on changing the allocated DHCP address range, but rather want to move some of the reserved and excluded DHCP addresses out of the address pool.

e.g. printers will be 192.168.2.x

I will obviously need to change the subnet mask manually on my manually configured devices.

Answer

Maybe not the best design:
Are you sure that is the route you want to go? It should work fine, but then you are using the entire 192.168.x.x network for one broadcast domain. That is going to give you 65534 hosts. If your company grows, you are going to have re-subnet the entire network again or start using 10.x.x.x or 172.16-172.31.x.x address.

A More Standard Way to Approach it:
I think a more normal approach be to use a subnet per location, or office floor, etc.

1. Start with how many machines might
   end up at each location and then
   maybe bump up to the subnet above
   that.

For Example:
So if you think you might have 254 devices on the network per area, bump it up to 255.255.252.0, the next subnet up. This will give you a host range of 192.168.0.1-192.168.3.254. Then when it becomes time to expand, the next range using the same subnet mask would be 192.168.4.1 to 192.168.7.254.

A Simple Way:
A simple way if your office is small, would be just to set the DHCP range to something like 192.168.0.1-150, and then use the rest of the IPs in that address space for static assignment. Your DHCP server should have the option to specify a host range to hand out that doesn't line up with network mask. And if it only works by subnet masks, you could always cut the subnet in half with a mask of 255.255.255.128.

A Good Subnetting Read:
I recommend reading Evan's answer to How does Subnetting Work, and How do you do it?.