I did a bit of research and below are my findings around it.
1) It is not MUST to have a view but it is always good to have a View.
2) A report is created to bring to life the data and analysis that business needs. However, a view is that subset of this big report that business will use in day to day basis.
3) A view is needed Mainly because A Report is generally a very big data set - which can have one or multiple Data sources in combined or joined fashion. However, business may not need all those attribute to get the analysis out of it, rather they would need this data tailored to their reporting need. View exactly gives this opportunity to tailor the vast amount of data from a large report into smaller reports - which are also called as Selection views.
Regards
Suchita