Seed is formed during sexual reproduction. Sexual reproduction creates more variation. Thus seed formation is advantageous as there are chances of survival in changing surroundings.
Seeds can get dispersed into new areas, and this prevents a species from going extinct.
The seed contains the future plant or embryo which can develop into a seedling under appropriate conditions. The seed is in a state of dormancy and can be kept in a secure state for a long period of time. the seed contains three generations.