If you set reservations in the DHCP for specific machines or printers, then DHCP would still handle these, it would know that these machines(mac addresses) have assigned IP addresses and they will always get that address. These reserved addresses are within the DHCP range so you wouldn't need to reduce the DHCP range if you just set reservations. These reserved IP adresses will not be available to lease out to other machines.
How many devices do you have on your network? Are there a lot of mobile(temporary) devices? Reducing the lease time may help free up some addresses.