Toolkits can be useful when you want to better organize your inventory of assets and check out groups of assets without having to select them all one by one. For example, you may have a toolbox that contains dozens of tools, this toolbox may be part of a truck (which can also be considered as a "toolkit"), this truck may contain many different other toolboxes, etc.
So, as you can see, the "Toolkits" feature will help you organize your tools in a convenient hierarchical way.
You can create and manage toolkits from this view :
When creating a new toolkit, use this drop down list to select it's parent toolkit (if any) :
Let's go back to the asset's list :
Now when performing a check out or check in operation, you can select one or more toolkits to add to the list of assets to check out :