I know there is already a discussion about suspension lefty forks. However, that post completely avoids mentioning of their rigid counterparts which also can be found in the wild.
Below is a couple of photos of rental bikes commonly used in Singapore.
[While looking closely at the second picture, I have realized that there is also just one rear dropout!]
Searching through the net gives other examples of rigid leftys:
EDIT Added more examples.
Vintage 1910's bike:
Somewhat's newer one:
So, what's the deal with them? What are advantages, and there must be some disadvantages (like less compatibility with fenders, hubs, rim brakes etc.)?