A practical decision
Use leave-in with rinse-out conditioner only when it adds a job
You can use both, but decide what the leave-in contributes before adding it. A rinse-out conditioner handles the wash-day conditioning and detangling step, then is rinsed away. A leave-in remains on the hair and may add detangling, manageability or an exact product’s styling-preparation benefit.
Keep the successful step
If your rinse-out conditioner already works, keep it while evaluating the leave-in. Replacing both at once makes it harder to understand a change in feel. Follow the rinse-out directions completely before applying the leave-on product.
Check whether the bottle allows both modes
Knot Today is a useful example of product-specific directions: its maker permits rinse-out use for wavy hair and leave-in use for thicker curls. That permission belongs to that product. Do not assume every rinse-out conditioner is designed to be left on.
Stop at enough conditioning
If the added step makes the lengths easier to manage and you like the dry feel, it has a job. If you cannot identify a benefit or the layers feel coated, review the addition before adding another mask or cream. Keep notes about the exact bottles and the result you want.
Review the named products and manufacturer sources, then make a care card.