The following information is provided by Gyuto Monastery.    

Why Have an Altar?

A proper altar holds images or representations of the Buddha's enlightened body, speech and mind which serve as reminders of the goal of Buddhist practice; that is: to develop these qualities in oneself so as to be able to fully benefit all sentient beings.

The reason for setting up an altar is not for fame, for showing off wealth, or to increase pride, but rather it is to reduce one's mental afflictions and to seek the ability to help all sentient beings.