Credit card companies sometimes offer rewards like Air Miles, Nectar points or cash back. But, the real awards tend to be only available if you clear your balance every month.
If you move to a new card with rewards, you will find that you need to spend over a certain amount in the first month in order to reap the rewards, encouraging you to spend on your card and increase your debt to them.
If you have a rewards card, make the most of it by using it only for your everyday purchases or company expenses and pay the full amount each month. Never keep a balance on a rewards card.