[andresont]

My tank was without the sump for 1.5 years.
Now i got one too , because i wanted to have Zeo ,to hide all the heaters and other equipment etc.
Extra water volume isn't that much difference, because it gets dirty as the rest of the water very fast, but larger water volume is more forgiving for sure.

( I just copied this from the Mark's article above for easy reference)

Sumps have many advantages:

Increased total water volume - This dilutes the pollutants that accumulate in your tank’s water, and helps to slow issues that arise quickly in sumpless tanks.
-Skims the surface - No more surface scum, just crystal clear water.
-Lowers temperature - I've observed a 2°F drop in temperature after installing a sump.
-Hides equipment - Heaters, protein skimmers, monitoring probes, grounding probes and more can be moved to the sump and out of the display tank.
-Consistent water level - The display tank will maintain the same water level all the time; evaporation occurs in the sump over time.
-Safe place to pour in additives - Adding chemicals or reverse osmosis de-ionized (RO/DI) water in the sump allows it to mix before entering the display tank.
-Increased circulation - The return water from the sump is yet another way to move water in your tank. You can point the return outlet(s) in different directions to create some flow, reducing the need for some of the powerheads needed in your display tank.
-Increased oxygenation - As water drains into the sump, air mixes with it, allowing for beneficial gas exchange -- releasing CO2 and adding fresh O2.
-Refugium on reverse lighting - Helps maintain pH levels during the late night hours.
.