Cat urine has an extremely sharp and pungent smell that can often stay for hours if not properly gotten rid of. It is really important to clean the kitty litter often because if the cat urine is allowed to remain there and decay, its smell will become even worse over time.
It is easy to clean the kitty litter if you do it often. The smell is not as bad as it can be. Also, some cats are finicky and if the kittle litter is not cleaned often, some cats may pee elsewhere in the house.
In general, just as human urine is removed through the sewage system, so should cat urine be cleaned often in order to maintain proper hygiene in your home.