Precisely!
A lot of people have the misconception that just because they received an ATAR lower than expected, that they can't get into their desired course. This is a myth. I repeat, this is a myth. The lowest selection ranks that are provided for your courses are just estimates and are variable to how many spots they have and how many people want to get into that course. This means even if your ATAR is lower than the lowest selection rank, there's a chance you can still snag a spot in your most desired course.
If you received an ATAR lower than expected, the game plan should be as follows:
Preference 1: [course you wanted to study the most, regardless of ATAR]
Preference 2 - 7: [any other courses you really wanted to study/ your back ups] or if you don't have enough courses to fill this out [courses that your ATAR will permit you/ will likely be able to get in]
Preference 8 (and maybe 7): [courses that your ATAR will permit/ will likely be able to get in]
On the other hand, if you received an ATAR a lot higher than you were expecting, don't change your preferences simply because you think you're "wasting your ATAR" if you know that course is not what you truly want to study.
One last tip: Make your Preference #1 what you truly want to study. If you don't want to study it, don't make it your first preference. Some people think that because their family, friends or relatives are encouraging them to study [insert course here] that this should be Preference #1. This is false. You're the one who's going to spend their time and effort into a course. You might as well find one that you actually enjoy.