Owners of sebum-deficient type of skin (dry) and if you have dehydrated skin, then you must cover this serum with a cream. In other cases, you need to focus on air humidity and individual feelings.
If the air humidity is below 40%, then this serum should be covered with a cream, even for owners of very oily skin.
If the air humidity is higher, you need to focus on the feeling after application. You can try using the serum without cream for a couple of days, if you don't feel tight or stiff, it means you have enough of it. But please note that this humidity (40% and above) is usually in the warm period, which means that the activity of the sun is higher, so do not forget to use sunscreen when going outside.