Are all of the Errors important in a project??
And are MissingReferenceException Errors important?
In short, yes.
There are 3 types of feedback. Errors, warnings and notifications. Errors are always important. Warnings are sometimes important. Notifications, not so much.
The missing reference error message means that there is a gameObject or script or component etc that you have explicitly designed to use but the game cannot find it.
What is the exact error message you are receiving? Copy and paste it from your console.