Every horse I see I always find the saddle fitting landmarks and chalk them on. I also show my clients how to find them and encourage you to take a photo of them to help you remember.
Majority of clients I see sit their saddles too far forward over the shoulder. This restricts the front-end movement and changes the balance of your saddle. It can also over time cause damage to the cartilage of the scapular. Sitting your saddle too far forward over the shoulder can also cause postural changes and could lead to sway backs, hollowing in wither pockets and tension in the lumbar area.
If a saddle fitter ever tells you just to slide the saddle back to where it stops, that is an incorrect way to find where you saddle should fit, as it depends on the shape of the horse and saddle how far it will slide back.
Learn how to find the saddle fitting landmarks your self and you will be more accurate and have a more comfortable horse. I have videos of this on my website as well.