Perlite is commonly used in potting soil and soilless mixes (particularly for indoor seed starting) to keep the soil structure loose and well-draining without risk of compaction over time.
You can combine equal parts perlite, vermiculite, and peat moss (or coco coir) for a clean, basic seed starting mix that supports healthy seedling development and reduces damping off disease.
You can also use it to propagate plant cuttings. Rather than just rooting your cutting in water, you can root it in a small jar filled with moistened perlite.
The same goes for seeds: start them in moistened perlite only, or test the germination of older seeds in baggies filled with moistened perlite.
In raised beds or in-ground garden beds that have trouble with cakey clay soil, you can improve drainage by raking in a 2-inch layer of perlite into the top 6 to 12 inches of soil, at the same time you amend the soil with compost and other nutrients.