Proxy media

The editing application generates them once, you cut against them, then it switches back to the source files for the export, so nothing about the finished quality changes. Premiere calls them proxies, Final Cut talks about proxy and optimised media, Resolve offers both. This is what makes 4K, high frame rates and heavily compressed camera codecs workable on a laptop that would otherwise stutter. The costs are disk space and the time it takes to build them. Two things to watch: grade against the originals rather than the proxies, and check the timeline has switched back to full resolution before you hit export.