A few things to be aware of:
Seed is the number 1 way that pathogens, insects and weeds are transmitted around the globe.
Do NOT save seed from unhealthy looking plants. Many viruses, bacteria, and fungi can be transmitted via seed.
Make sure you know the proper sanitation procedures before sharing seeds. For example all tomatoes seeds need to be extracted via acid extraction to prevent transmission of bacterial canker. Pepper seed need to be treated with a TSP bath to eliminate TMV. All cucurbits need to be treated with a peroxide to eliminate bacterial fruit blotch.
Be sure you know 100% what you are harvesting is the seed from the plant. Many weed seeds look identical to many common garden varieties.
Know the basic reproductive biology of the species you want to save. This can help to unintentional outcrossing and mixing of varieties..
Please save seeds from F1 hybrids. Selection from amanteur seedsavers/breeders have maintained/generated some of the most important traits we have. Feel free to make your own crosses introgressing important resistant genes into landraces.
Before sharing carefully inspect the seed to ensure you have no unpleasant hitchhikers in the seed. An observational microscope can help with this.
It's a butterflybush. Just cut it back to where you want it to be. They are extremely hard to kill.