Depends on your hardware and how much space you have for radiators.
For example... it makes not really sense to cool a CPU with less than 65W TDP with water. But if you have a CPU with more than 100 W TDP, you will have a big difference between an air cooler and a water cooling system with a 360 mm ST30 NexXxoS radiator and an Eisblock XPX cooler.
for a gpu i can give you a concrete example, i have a 1080ti strix , when gaming in 4k60 it ran on air at 78c with VRM at 98c , with a gpu block on the card is 40-45 and VRM is 55c under gaming load so i dropped basically half my temps when Watercooling, granted i have some serious radiators in my case , but its without a doubt if you have powerful parts worth it . but if you are using a 1060 and i5 9400 you would be just fine with air .