My computer isn’t that good, so the playback has really low FPS (with a lot of filters sometimes as low as 5 FPS). That isn’t very practical if you want to edit video’s. I know Vegas Pro 17 (and I think Premiere Pro) have a feature to reduce the playback resolution and even FPS. This would be a very helpful feature for people without good computers.
This very feature is coming in the next version of Shotcut which will be released in about a week. It will be called “Preview Scaling”.