To each his own: on the market there are in fact various types of products.
In short, to each his own. In fact, there are various types of products on the market. The most traditional are the so-called "rinse", to be applied after shampooing on the very wet head and then rinse thoroughly. There are both for normal hair and for oily hair.
Then there are the no-rinse balms, in technical jargon called "leave-in", particularly suitable for those who need a product that acts quickly. These must be applied before towel-drying the hair and before drying it with a hairdryer.
The difference between the two types, however, is mostly practical. Thanks to their quick effect, the "leave in" is perfect after the swimming pool or the gym, when you are running, but also for those who wash their heads every day.
Instead, according to experts, it is better to avoid the very fashionable products in recent times: the so-called "shampoos plus conditioner, 2 in 1". The functions of the two products, in fact, are antithetical: if on the one hand the shampoo must remove, on the other the conditioner must restore.
The shampoo is made to wash the hair, removing dirt and inevitably also the sebum, while the conditioner must act on clean hair, giving back what good the washing has removed. It is impossible to condense the two functions into one product.