Why is maintenance of a software important?
The alteration of a software product, after delivery, to correct faults, to improve performance or other attributes, or to adapt the product to a changed environment.
Maintenance is a significant part of the software life-cycle. It is costly in manpower and resources, and one of the aims of software engineering is to decrease its cost.
The most significant problem during maintenance is the before correcting or modifying a program, the programmer must first understand it.