Restrict Access gives teachers some extra control over resources and activities that don’t have built in due-dates such as Forums. (Though this will prevent students from seeing much more than their grade in the gradebook- they will be unable to see any posts made within said forum.)
You can apply open and close dates to any activity or resource and have it still show grades in the gradebook for students, it will however prevent them from viewing the content or otherwise accessing that resource or activity beyond the title and their earned grade. Activities like Quizzes and Assignments should use their built-in Close and Due-Date settings rather than Restrict Access (Date).
If you have completion tracking enabled in your course you’ll get an extra option of Completion under Restrict Access. This can be useful for enforcing an order of operations or ensure students show a level of competency on an assignment before being able to move on to the next item that builds on that competency. Some examples of this include making sure that students must submit a file before moving on, make so many posts to a forum before moving on, or receive a passing grade on a quiz (unlimited attempts) before being able to move on.
Be aware that items that are completely hidden from students will not count towards the grades students see which may not match what you see.
If the unmet visibility settings for an item with restrict access is set to show the grade item greyed out you and students will be able to see their grade and gradebook feedback but will not be able to enter the activity to look at content, work, or inline/file feedback.
If using more than one restriction with restrict access double-check with students that items are available when you think they are and that they do not conflict.