Is it essential to use both primary and secondary distribution Switchgears when we locally design MV system?
If - in a certain MV network - we can cancel either primary or secondary distribution Switchgear.
In fact, the quick answer is Yes, but this is mainly dependent on your application.
As an example, a very small shop/commercial activity can be fed via existing LV system. A small industry can be fed directly via existing infrastructure of ring-systems (basically secondary distribution network), while a heavy industry (e.g. cement/MMM....etc) might need a direct supply from primary distribution or - some times - via an HV/MV substation.
So to sum up, the main architecture mainly depends on power, energy, short circuit capacity of the required application.
In attached chapter (Network structures) you can find many practical typologies used worldwide stating the main use/advantage & drawbacks of each.