You should almost always have a clustered index. Each table gets one clustered index, but they do a whole lot by organizing it into an order for storage.
- Define how the engine interacts with storage
- Make updates, deletes, and creating indexes faster
- Enable deletes to free up table space (This allows your selects to skip this empty space)
- Prevent stored pages from “overflowing” and creating pointers to the overflow
- Allow for the raw data to be seeked into instead of scanned in entirety
- All selects will perform at least as good if not better
