Benefits for adding a sump:
1. Increases overall water volume - helps stabilize temp, water parameters etc.
2. Increases oxygen levels - by water flowing down the pipe and increasing the overall surface area of the water.
3. Because of the increase O2 and surface area, it helps stabilize pH levels
4. It holds all of your equipment and keeps your display tank from becoming cluttered.
5. Speaking of holding equipment - you can fit much larger protein skimmers in that area, that otherwise would not be able to fit on the back of the tank. It also hides your heaters and filters, which is a major plus.
6. It can hold a refugium with macroalgae or an algae scrubber. Either one will be a great method of nutrient export and management. IT would also increase O2 levels, and stabilize your nighttime pH and temp.
7. The larger volume of water from having a sump will prevent salinity and temp swings, which harm your livestock (including fish, corals and inverts)
8. More types of equipment are adapted for sumps such as ca reactors, kalkwasser stirrers, phosphate reactors, carbon reactors,denitraters, vodka filters, DE filters, ETC ETC ETC.
9. Replacement filters can be cut from blue and white bonded filter media, which can save you money in the long run by not having to buy filter cartridges.
10. You can install an Automatic Top Off Unit (ATO) which will greatly stabilize salinity, especially in such a small tank. They also don't add a whole lot of water to your system at the same time - so it has a long dwell time to mix the water before it's added to the display tank.
That's just a few things that I can think of off the top of my head.
