The "Technical Features" is a group that you can assign on users to give access to lots of technical information. Once you are in this group, you have more menus in each application (don't forget to reload menus after assigning the group) mostly for configurations. You also have more fields visible on most views.

As an example, on the user view, it shows all fields that are the groups this user can belong to. Most of these hidden groups are configurable through the Settings / ... menu. The tooltips on the checkbox fields in the Settings menus are more explicit about their business impact.

It's not very useful to assign such groups on the user form because it's much easier to configure such options from the Settings / ... menu instead. This will assign groups to all users and set the default groups for new users.

But you can still assign a technical group on a specific user if he should be the only one to benefit from this option. Example of options you find in these groups: "Allow to set a different address for delivey and invoicing on the sale order" or "Allow using different units of measures".