Why is defragmentation necessary?

Because over time, fragmentation of files on the disk occurs, i.e. to the fact that file fragments are stored in different, distant from each other sectors. which slows down access to files and leads to premature disk wear.
During defragmentation, files are written to sectors located sequentially one after another.

Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.