This depends largely on what species is being kept. Different species require different temperature ranges in their enclosure.
Corn snake and most colubrids for example, love a hotspot of about 28-30 degrees and a old side of around 25-28 degrees Celsius.
Ball pythons require warmer areas of between 30-32 ideally.
Most Asian rat snakes need cooler temps of about 25-28 degrees maximum.
Do plenty of research before obtaining your snake so you can provide the best care possible.