Sumps are more popular with reefer's and let you have a wet/ dry environment to grow denitrifying bacteria (search "bio-balls"). However, they are inefficient because the falling water has to be pumped all the way back to the top of the tank (and ends up requiring about 10X the energy of a canister to circulate the same GPH.)
A frequent complaint is gurgling sounds from the water draining down. This can be eliminated with the proper plumbing, but it will take some tweaking.
On the benefits side: You can set up a sump with every whistle-and-bell you can imagine. Virtually all the aquarium equipment can be setup and run in the sump and thereby kept out of sight. You also will maintain the exact same water level, regardless of evaporation (until the sump runs dry that is).
For the average planted tank, I'm not convinced it's a good idea:
#1. It requires a drilled tank w/ overflows. (There are aftermarket HOB conversion boxes, but you're at an increased risk of flooding)
#2. The main benefit of denitrifying wet-dry media isn't of much interest: Your plants should be the main consumer of nitrogen.
#3. You will need a fairly husky recirculation pump for this to work right
#4. There's always a risk of flooding the room if your overflow gets clogged.
#5. There's more ambient noise
#6. The splashing water will off-gas your CO2
#7. Increased electric usage, above-and-beyond your heater and grow lights.
#8. Requires a stand capable of storing a sump inside it.
For the only advantage of hiding the tank equipment and having a consistent water level...... I just can't justify setting up sump on my tank.
As per TPT protocol, everyone will now pile on me for being a moron!