Hi. A little summary.
Asset Bundles are not related to pooling in anyway. Here my general takes.
1. Asset bundles are used to load/install data for your game, that wasent installed during the initial install.
2. These asset bundles (of data), can be fetched from online or from your local device (iphone, PC, ps4, whatever).
Online
A common thing asset bundles are used for is DLC. This allows you to ship your game, but users can buy (or for free) get more content. Your game then makes a request to the pre-determined server holding your asset bundle, downloads it, and installs it.
I do a fair amount of translation, and a lot of dictionary apps for example don't install all the dictionarys at once. They allow you to choose which ones you want, and then download and install them. This allows apps on the app store to look/remain small, but then choose which big chunks of data you want to download later.
Local Device
Asset bundles are stored as compressed data (like zips). This can shrink file sizes. Your game may come with all the asset bundles within it already. But in order to make certain parts of your game smaller, they can be stored in asset bundles, and only unzipped if they are needed. This way nothing needs to be downloaded offline. (Or maybe you sell a super pack that includes all the DLC, etc).
Other
Basically asset bundles allows for some modularity. I am sure there are other uses that I have not thought about/read about. However, the playmaker actions plus some new tools that unity has been putting out, is making asset bundles easier and easier to use. According to some unity talks, improving asset bundles has been one of their main tasks these past few years.
A tutorial video or two is on my to do list for sure. If people do have any questions, please feel free to ask. Although I am not an expert, I may be able to help.