Banner or Header Photos
Parallax header designs can be very eye catching for those wanting their website to stand out and be seen. If you have a banner or header photo, it can be very cool to see your header picture change to a 3D eye-pleasing picture, so it can be great to use it for a main attention holder. Make sure to use it sparingly though, as repetition in this can get stale and lose its effect on your site’s design
Amount of Visits You Expect
Parallax scrolling works well only if your website doesn't need a lot of repeat business. Parallax should only be treated as something pleasing creatively, so don't expect it to help you gain a lot of users or drive in tons of traffic.
Mobile Usage
Remember that parallax is not very mobile friendly, so if this drives a lot of your traffic, it may be in your best interest not to use it. Only use parallax if you are trying to please customers through a computer, as this is the only way it will work.