I've created a Tracker improvement ticket that will reduce confusion and unexpected gradebook behavior on new instances of LTI tools. Please read it and vote for it here: https://tracker.moodle.org/browse/MDL-62839
Also, if you have a better understanding of Moodle code than I do, please feel free to contribute a patch!
When an administrator has configured an LTI tool and has set Accept grades from this tool to "Delegate to teacher", Moodle's default behavior is to enable that feature on all new instances of the tool. Moreover, on the settings page when adding a new LTI instance to a course, this checkbox is initially hidden in the "Privacy" section, making it very likely that it will be missed. Worse still, once grading is (unexpectedly) enabled, a new column in the gradebook will be created, which could cause confusion to students if the teacher did not intend for that to happen.
The solution to avoid all of this confusion is simple, and the new Tracker ticket merely suggests that Accept grades from this tool be unchecked by default so that grading in LTI instances is treated as "opt-in". Since there is no administrative setting for this option, a change to core code is needed.
Thank you for supporting this idea!