Subnets needed?

I’m new to networking. My predecessor recommended my company to break up our 192.168.x.x network into 3 subnets, 1 for the servers, 2nd for dept. A and 3rd for dept. B. We only have 40 users but are installing an VoIP system. Our vendor indicated there’s no benefit to subnetting here since we have plenty of IPs. Other than the number of hosts, is there any benefit to subnetting for a small number of users?

Thanks in advance!