What is the importance of senescence?

Importance of senescence :
(a) It maintains efficiency since the older, exhausted and inefficient parts are replaced by new, younger plants.
(b) Shoot senescence is a mechanism to help the plants perennate during unfavourable periods.
© The cellular breakdown results in release of many nutrients during senescence.
(d) Litter of fallen leaves and twigs is an important
source of humus and mineral replenishment for the soil.