If you don't want to show all files within category there should be possibility to select types you want from that categories drop down menu.

Another useful feature would be possibility to work with selected files as if they were only files in folder. Each time you select two or more files item “selected” will appear in filter bar (as shown below).

https://www.dropbox.com/s/e0xjf8j8heerw8c/4%20-%20selection.png

After you selected files you want just click item "selected" and only selected files will be shown (as shown below).

https://www.dropbox.com/s/ukrs74j4d19mxg3/5%20-%20selected.png

This option allows you to work with and open selected files without loosing selection. It could also let you to narrow your selection by letting you select within selection.

Each category can have it's default view (thumbnails for images and videos, list for documents etc.

For user who don't need filtering by categories like Documents/Images/Videos..., filter bar could perform other functions, such as: filtering by date modified, filtering by size etc. For folders with only one type of files filter bar could automatically switch to another filtering method.

In short, advantages of filter bar are:

1. Gives you instant information on categories of files the folder is containing (no need to sort and scroll down). If folder contains music you will instantly know it – just take quick look at the filter bar.

2. You can filter files with a single click and quickly switch between different categories.

3. Allows you to work with selected files as if they were only files in folder.

4. Reduces need to switch file view (thumbnails, details etc.) – each file category can have its default view (e.g. thumbnails for images and videos, icons for documents etc.).

5. Reduces/eliminates use of scroll bars – reduced number of files in a pane reduces need for scrolling.