When you convert a VM into a template, if you choose not to compact it, you can easily convert it back to a normal VM and back to a template, if you ever need to make changes/updates.
The benefit of using a template over cloning is automation. By automating the process of building a new VM from a template, you greatly reduce amount of time and amount of possible errors/mistakes during provisioning.
For example, when I build a new VM from a template, after selecting the datastore to use I can walk away and the VM is automatically cloned, powered-on, computername set, domain joined, VM tools installed, etc. It's really a set-it-and-forget-it process.
If I did not use a template, I'd have to manually clone, disable NIC (OS conflicts with cloned names on same network, etc.) power-on the VM, copy sysprep files, possibly modify sysprep.inf, run sysprep, reboot, reconnect NIC, join domain, reboot. No automation means I'm spending too much time provisioning one virtual machine, and I have to hope I didn't make a mistake somewhere in the process.