You do not need to follow this or most other MVC conventions, but we recommend that you do — not least because it will help you make sense of the examples in this book.
Not least means it's important.
used for emphasizing the importance of a particular aspect of a situation
George is an excellent manager, not least because he is genuinely willing to listen.
Not least among our difficulties is our lack of funding.
It might be easier to understand your sentence like this:
You do not need to follow this or most other MVC conventions, but we recommend that you do. And, that is important because it will help you make sense of the examples in this book.
The definition in DamkerngT.'s answer gives the essential meaning of this phrase, but it may be of value to describe how the phrase means that.
Least here is the opposite of most or greatest. There is an implicit scale of importance or difficulty running from the least important reason or least difficulty to the most important reason or greatest difficulty. Not least marks a point on the scale that is higher than least but not necessarily as high as most.
The author thus employs the form not least because in order to express that
- There are several reasons for following the conventions.
- One reason is because it will help you make sense of the examples.
- Other reasons may be more important in certain circumstances.
- But this reason is never the least important.
It is a key role of management to anticipate future developments, not least when things are going well.
Thatcher's spirit lives on, not least in self-reliant Hong Kong.
Pay rises must be sustainable in the long term, not least after WCS funding ends, so it is important to tie them to productivity.