There is no added security with Clientless webvpn, just ease of management. Both clientless and Anyconnect client based VPN use TLS tunnels to pass data. And both can be have filters to restrict access to only whats required. The advantage of clientless is the ability for a third party (contractor, vendor etc) to connect without a need for a corporate software like Anyconnect. Since most of the apps can be made web-based, this allows for easy and secure access without the overhead of providing these users with a software to do anything on your network.
