Hey,
without vCenter you can basicly just create and run VMs.
Most other functions, like HA,DRS,vMotion,SvMotion,SDRS, etc. require a vCenter Server.
If you can afford Enterprise Plus licenses, buying one vCenter Server Standard license will not ruin you :smileywink: (Or the cheaper vCenter Server Foundation, which can only manage up to 3 ESXi hosts)
Regards
Tim