Both are important. Every business wants to maximize their sales and the profits on each. You will find some business owners that believe it is important to turn inventory quickly and will work will a smaller markup to turn product quickly and then there are those that will mark it up and hold it until sold.
Walmart for example will bring an item in at a reasonable markup, but if it is not selling will mark it down until it sells and then replace it with an item that sells better and faster at a better profit margin.
Good luck and best wishes.