Is validation required for clustering? If yes, then why is it required?

Clustering algorithms have a tendency to cluster even when the data is random. It is essential to validate if a non-random structure is present in the data. It is also required to validate whether the number of clusters formed is appropriate or not.

Evaluation of clusters is done with or without external reference to check the fitness of the data. Evaluation is also done to compare clusters and decide the better among them.