The summary of the preference is:
| Toggles access to certain Adobe services in Acrobat products (varies across versions) other than shared reviews and forms distribution. |
So it toggles all service access off and on for both Acrobat and Reader. EchoSign is a service, and those other signature options you see (all but "work with certificates") are part of EchoSign workflows.
You can change the pref value to one or just delete it altogether.
hth,
Ben