Whitening can be of different kinds. A basic scaling and polishing often makes a huge difference in brightening teeth. It helps to remove plaque and stains thus making teeth shine. It is a mechanical process. However, this doesn't change the actual shade of your teeth, only brightens them. Bleaching is the use of chemical bleach agents to change the shade of your teeth to a whiter one. It is recommended if your dentist feels there is scope for the same. Both have different benefits abd results. Visit a dentist to decide what suits you best.