While wearing a suncreen or a moisturizer with SPF in essential in summer it can be important to wash it off in the evening. While it might not be necessary to use a separate night cream to moisturize, one of the reasons why you would is because you might be using one with SPF protection.
A moisturizer or lotion with SPF should only be used in the day for obvious reasons. If you apply a moisturizer with SPF in it at nigh you risk having your pores clogged in the long term. Remember that your skin is repairing itself at night so it’s better to use a moisturizer formulated to improve the skin’s function.