There is no built-in option to turn off the display of that column. You could always use some targeted CSS to change visibility to hidden or display to none for those cells. That’s about the only way you could do it right now, without writing a more complex function to tap into the filter hook that already exists for filtering the signups retrieved from the database for display (you would have to hook into that filter, loop through the signups and set the signup->item property to an empty string). Or, to completely hide the details column and all entries, you could tap into the filter hook that filters the retrieved tasks for the sheet & date, loop through the tasks, and set all the need_details properties to ‘no’, or anything but “YES”. If none of the tasks have need_details set to “YES”, then that column won’t even be displayed.
I’m getting ready to release an update to the main plugin, as well as the Groups extension, to allow a sheet to be assigned to more than one group, and to also allow the ability to restrict content to members of groups (either via BuddyPress or the WordPress Groups plugin), so I could probably throw in a filter hook on the output of those details, which could be used by other plugins (or a simple function in your theme’s functions.php file) to return a blank value (empty string) so it’s not displayed on the front end. Hoping to have those updates released within the next week or two.