They are felt as well as imagined. They provide an indefinite background or aura to the foreground of the actual situation. Spontaneous release of energy, feeling, emotion, personal interest. Impulses are infinite in number and vary within each individual. It is the basis of invention, creativity, and play.
Habits are a well oiled machine, and impulses are random outbursts.
A balance of both is required for human conduct. Each individual is a unique organic outgrowth of myriads of common physical and societal conditions. Out of the common and the shared the unique and particular arises. This is true in all of nature, and it is true of human beings as well. The variety of the universe is the outgrowth of transactions between common factors.