What are Categories used for ???

JosieNurseTN Categories are the names of the templates your items were created from. They are names of the blueprints that define the default fields within an item. If you create a new item, you choose a category and get a default set of fields to fill. If you imported from Lastpass, your existing items were apparently assigned some category, probably according to how they were created in the first place in Lastpass. The vast majority of items will probably be the "Login" category, the template that combines a username, password and URL for website login.

17 vaults seem a bit excessive. It seems you mistake vaults with what tags are made for. Vaults are not meant as organizing or managing scope, not meant as folders where you add all similar items.

Instead, they are meant for access control and access separation. There is real functionality attached to them.

You use vaults for family accounts if you need to share items between some but not all members.

And you use vaults on a standalone account if you have (for example) a vault full of business accounts you use while working and another vault full of private accounts you use out of work only. To avoid private accounts show up while doing business work and vice versa, you create a collection for work and add only your work related vault. And you create a collection for out of work and add only the vault with private accounts. Then you switch between work and out of work collection if you switch between work and out of work.

If you're travelling and want some high security items not be stored on a mobile device, you can put them into their own vault and not sync that vault to that device or use this vault with travel mode.

But usually, you put all items in only one vault and for sorting and organizing use tags. In settings, activate tag display in the sidebar, optionally disable category display, and you're perfectly organized. You can create nested tags by using the / character within the tag name.

Since you can add as many tags to an item as you want, so an item will show up within every tag you add to it, this will also solve your reused password issue, since you only keep one item and not duplicate it into multiple vaults.