If you're talking about leather in cars, then NO don't do it.
Most leathers are coated for protection and durability.
The best way to clean: Woolite! 6:1 mix and you have one of the best cleaners!
Adding a conditioner is very subjective. I use Zaino Z-10 as it smells the closest to new leather.
Some treatments are too oily/greasy. You want one light on that aspect unless you're doing old leather.
Regards,
Deanski