I would say there are three mayor criteria to consider. Please be aware that I'm only covering semi-large to large screen usage in this answer, I think that the following rules don't apply for smartphone- or "phablet"-screens.
1. Compactness of lists
This is a rather easy one: If your list items contain text and are thus wider than high, it is much faster for a user to scan the list for the action he wants to activate:
If your list is horizontal, you have to visually travel the width of every element in order to find the desired one.
With a horizontal list, you can jump from one element to the next as soon as you determine that the current item you're looking at is not the one you're searching for.
Of course, as soon as your list only contains icons (which is generally a bad idea), this doesn't apply anymore.
2. Screen estate
This is a huge one on desktops and tablets, not so much on smartphones though. As those "large" screens evolved to wider aspect ratios, and users are accustomed to vertically scrolling content, you need a way to use screen estate as good as possible.
This means, in order to give the informational content as much estate as possible, it has to use the full screen height. So, in order to account for that, you'll have to move any action toolbars and navigational links to a sidebar.
An additional benefit of this is that you're reducing distractions from the content itself.
Also, if your list contains a large amount of items, you probably don't have any other choice but to use a horizontal list. A scrolling horizontal list should be avoided if possible.
3. Visual hierarchy
Now we're getting to the tougher one, which is also dependent on your situation: If your actions are global to the current view and not bound to a certain object that could move out of view, you should keep those actions in a sidebar or a header. Because of reasons already discussed, a sidebar would be the better choice. As we are conditioned to conceive the content from left to right, a sidebar on the left clearly stands out as a global navigational tool and can divide your view nicely.
But, if you have actions bound to a certain object, they should definitely stay in range of it, and that's where things get blurry. I would still mainly consider a horizontal list, but in some cases vertical lists (for a small amount of actions to group) or grids could work just as fine.
Conclusion / TL;DR
So yes, a vertical list offers a lot of benefits over a horizontal one, especially on widescreen devices and are vastly superior for a high amount of elements and elements with descriptions. That said, if you only need about three actions in your list, a horizontal list seems kind of like a waste of space, though, on the devices I considered, vertical space is way more valuable than horizontal space.