On iOS, you can shrink a project's storage and archive finished projects: see How to Optimize and Archive a Project. The tips below help on any phone.
HD video adds up, even in short snippets. Here are a handful of tips from the 1SE community.
Within the 1SE app
Turn on space optimization for your active projects to save up to 80% of storage space. You can also archive finished projects and offload them to 1SE Cloud. See How to Optimize and Archive a Project.
Delete the original videos you took your snippets from. Your snippets in 1SE are not connected to those source videos.
Be mindful of keeping many projects, like Freestyle projects for trips or weddings. Mash those projects to create a video to share and remember, then archive them to save space.
Within your iPhone's settings
Some camera settings can increase the size of your recorded videos. For example, using 120 fps on slo-mo videos, 4K at 30fps, or 1080p HD at 60fps with your phone's camera will take up more space.
In the Photos settings, turn on Optimize iPhone Storage to replace full-resolution photos and videos with optimized versions.