Please note: "Parallax" is both the name of an Out of the Sandbox Shopify theme and a generic name for a scrolling effect that is popular in web design (see this Wikipedia article for details).
If you enable the parallax scrolling effect in your Parallax Shopify theme, you will notice the effect does not work on tablets or mobile devices.
This decision was intentional because the parallax effect can cause significant performance issues on mobile and tablet devices, including "choppy" movement or even crashing the user's browser app. Therefore, in order to have a more seamless experience on tablets and mobile devices, the effect has been disabled (but the images are still visible and can be cropped or shown fully as needed).
The scrolling effect can also have a negative effect on user experience on mobile devices.
When exploring the parallax user-experience on mobile, Jay Eckert states:
One of the largest criticisms of the parallax scrolling effect is its poor performance on mobile devices. Parallax effects appear broken or choppy on mobile devices because mobile web browsers are designed to limit script execution upon scroll events.
A good web designer will understand this in advance and plan for a static or mobile-optimized version of the website that essentially “turns off” the parallax effect when the mobile environment is detected. The website will look exactly the same in its static state, we just remove the movement of design elements and the requirement of the mobile browser to call external scripts to perform the calculations their desktop cousins can do more easily.
Paula Scerbinina states:
As the technologies develop faster than anytime before, one of the downsides of the parallax scrolling effect can be not responsive. This means that not all browsers and devices may support the technology of the effect.
It is crucial to know parallax may not look the same on a mobile device or tablet as it does on your computer.
Plus, slow load times and even longer scroll together with the above-mentioned one can be the factor that impairs mobile viewing experiences.