Here is one chart I used long time ago to understand this
Anyconnect Essentials
Does not support CSD
Does not support Clientless
Only supports AnyConnect client connections
Anyconnect Premium
Does support CSD
Does support Clientless SSL VPN
Supports all flavor of SSL VPN: Anyconnect, clientless, All advanced SSL features.
The Anyconnect Essentials is a license that allows you to connect up to your 'Total VPN Peers" platform limit with AnyConnect.
Without an AnyConnect Essentials license, you are limited to the 'SSLVPN Peers' limit on your device.
So basically it's one or the other
How to enable the Anyconnect Essentials:
conf t
webvpn
anyconnect-essentials
Regards
Julio Carvajal
Senior Network Security and Core Specialist
CCIE #42930, 2xCCNP, JNCIP-SEC