Multiple virtual switch for specific set of VMs without physical connection will serve the local connectivity only, means VMs within a ESXi can communicate to each other but not to other segments in your network. It's better to create one Virtual Switch with multiple port group having a trunk uplink connection if you want to segregate your VMs to multiple networks.
If you want to communicate to other network outside your ESXi then creating multiple switchs requires multiple uplink physical connectivity.
Rest depends on your network architecture how you want to design it.
Regards,
Sachchidanand