Basically it works great for mass adding entire segments of the market to your quickbar. Items that are all in the same market category like for example, skill books. It doesn't work very well for doing things like adding all Caldari Navy modules because they're scattered all over the place in many different market categories.
For example I recently redid the skill book section of my quickbar to look like this:
In the past I'd always added items to my quickbar one at a time and then moved them into folders. This time I decided to do it differently. I simply opened browse, right clicked the "skills" category and added the entire "skills" category to my quickbar.
Then I opened the quickbar and went through all the skill folders, removing all the low priced books I don't deal in. Basically everything priced under 1 mil at school stations.
Note: for a new trader who doesn't have much ISK yet, I'd recommend moving the cheapest books into a "< 1 mil" folder and concentrating mainly on those at first, particularly the ones worth 90k - 1 mil. Delete them later when you have enough ISK it isn't worth your time working the cheap books anymore.
Next, I made 2 new folders, < 5 mil and 90 mil +, for the cheapest and most expensive books. There are 184 skill books I trade. I moved 43 books into the < 5 mil folder and 27 into the 90 mil + folder leaving 114 others in their original market category folders. I left the 20 subsystems books (5 mil books) in their original folder because it makes sense to me to keep them together yet separate from other 5 mil books.
The 90 mil + folder makes it quick and easy to check the most expensive books on any character. The under 5 mil folder makes it simple to ignore the cheapest books on characters that deal with more than just skill books and don't have enough orders to cover all 184 books..
The 2 new folders are incredibly useful, far more so than I expected. They really help streamline my routine and make checking the skill book market on different characters in different locations a whole lot easier. In fact it's working so well I'll probably make another folder for skills worth 5-10 million ISK soon and I might start putting some mods and implants into low and high value folders too instead of grouping them all by faction (mods) or type (implants).
Also see copying market quickbar settings to copy your settings to other accounts.