It's in the manual i believe.
it is recommended if you are not using top tier fuel, not needed but cant hurt if you are using top fuel.
Im looking to buy a 18 Elantra Sport but am currently driving a 2017 Sonata Sport 2.0T and it is the same GDI setup.
The only way to minimize the possible carbon build up is a catch can, oil changes with quality synthetic oil, and use of an occasional intake cleaner (not poured into gas tank) must be one of the ones that are sprayed into the intake.
BG makes a professional system that works well , but you have to go to a mechanic that has it and normal cost is about $ 150
CRC has their GDI Intake Cleaner, it is an aerosol of PEA and other chemicals (supposed to be 150x stronger than fuel additives) costs less than $ 15 and you spraay into intake before the turbo with engine rinning so it cleans up the turbo blades and the intake valves, they show pictures that it helps break down buildup, I believe that if used before any buildup starts it will keep things clean. ive used it 2 x in 25,000 miles and Ill drop a can of BG 44K or Techron in the tank at every oil change (5,000 mi)
This is a potential problem with GDI