Progress indicators, or “loading spinners,” indicate content is loading and users must wait before continuing to use an app.
Optimize the watch speed by using spinners only when waiting for a server in the cloud, like for search results, but not for local computations like calculations made by the watch itself.
If the user is waiting for a watch-based activity, avoid using progress spinners because they actually increase the wait time for actions to complete. You may use spinners for internet-based activities.
Instead of progress spinners, use launch screens with placeholder UIs or branded content. Launch screens prepare users to engage immediately as an app starts by familiarizing them with the content.
The Material Design spec describes progress indicator behaviors and states in more detail.