Single foot line guides were developed to reduce the overall weight of the rod. This might be something to consider in extreme cases of very large rods - especially when you're making a large surf rod or a really heavy bait casting rod. For fly rods, I feel that the weight isn't really an issue. Sure, they might be a little lighter because there's only one thread wrap used to secure the guide, but I don't think it's that noticeable where the 'rubber meets the road' along the stream. That small amount of weight reduction probably isn't really going to be noticed if you're using the rod for the usual fishing situations.
Single foot line guides do cost a little more, & thus add to the cost of the rod. They are also a little more tricky to put on a rod. At first you wouldn't think so, but lining up all those guides with only one foot is harder to do than the normal double footed snake-style guides. Plus, it takes a little more practice wrapping the one guide foot - securing it to the blank while wrapping it with thread. In fact, if they are not installed on the rod correctly by the rod maker, they will eventually come off the rod. Great care has to be taken to make sure that the guide foot is secured to the rod properly or there will be trouble in the future.
If you were making a rod solely for the purpose to cast great distances, like a tournament rod, then you might want to think about using single foot guides with ceramic inserts. These are guides that actually keep the line from touching the rod blank, & so reduce friction. Also the ceramic surface is slicker, & would allow the line to shoot better & further reduce friction. However there are rules in tournaments & you'd have to make sure such a rod was legal to use in whatever competition you were having it made for.
There have been many rods made through the years just for distance casting in tournament, but that's all these rods were made for. I don't think there's many of these "specialized" rods that you would want to take fishing because they lack other necessary characteristics that become extremely important when a fish is on the end of your line.
So, in my opinion, if you choose to have single foot guides on your rod that's fine. Unless you're getting a rod that's either very big or very small / light in weight, choose them because you like how they look. To me they can look stunning on a rod - if they fit into the overall aesthetic theme of the rod. For most of us, myself included, I don't think you'll be able to notice that much of a difference in your normal fishing between the two styles of line guides.