The primary reason you're probably considering an SSD hard drive is speed. Installing one in your PC or Mac can lower the boot and shutdown times dramatically. Plus, your apps will launch and run faster, and you'll see faster file transfers. Solid state drives, because they have no moving parts, tend to be cooler and quieter than hard drives. They are durable, shock-resistant, vibration-resistant and reliable.
The trade-off to all of these benefits is both cost and size constraints. Traditional hard drives are significantly less expensive than solid state drives. But keep in mind that installing an SSD drive in a slow older computer may ultimately be less expensive than buying a new computer. If you have a great deal of data to store, you may end up paying a high cost for an SSD. They are commonly available in sizes from 500GB to 1TB, while high-end systems may contain SSD as large as 4TB at a much higher cost.