By default opencart has a feature the one allows to register/assign customers to customer groups.
Once user registers to one or another group, you as admin can set for these groups different special prices, quantity discounts, reward points...

So why not to expand these functionalities more?

This module will allow you as admin to restrict or give access for specific group to categories and products.
That is you can block any category to be browsed by one or another customer group. Also you can set which items can be viewed / purchased by these groups as well.

this will put your opencart store to a new level. From now you can have a VIP users the ones can see completely different products on your store for different prices, or you can have a specific categories and product "packs" for wholesalers to be viewed and purchased, while regular customers will not be able even to see it:)

This is a must to have extension for those who wants to control every aspect of their shop and to be as flexible as possible:)

PS: Multilingual, multi shop supported, easy installation (no core files overwrite).