Dipoles/open baffles have a couple of benefits, compared to monopoles
- The interact "less" with the room; meaning cause less standing waves and reflections, the backwave even works for spaciousness.
- Have no internal issues with cabinet resonances/reflections, no non-linear behavior of damping material in the cabinet as well as provide symmetrical acoustic load on the speaker. A cabinet always provide some non-symmetrical load on the speaker = distortion
But like everything in physics, there are always caveats.
Efficiency of open baffles goes down rapidly and drastically beneath the "baffle-step" point.
This heavily depends on the (wave)length between the back and the front.
So in other words, it depends on the size of the baffle they are mounted in.
Often this results in big and wide baffles.
But so much so, that it is really hard and expensive to do anything substantial beneath 40-50Hz.
Even with a double 12 inch, or like 15 inch etc.
Definitely not suitable for any higher SPL applications.
This cancels out some of the earlier mentioned benefits quite a bit.
Because it means the same speaker has to provide (a lot) more excursion and power to get the same amount of SPL.
More excursion always results in more distortion.
The first mentioned advantage can also be taken care of with a multi-sub system.
Actually, this will often give a better and a much more predictable result that can even be easily tuned.
(especially these days, with free software and cheap mics).
The distortion from uneven loading in a closed cabinet is also not as bad, and mostly 2nd order distortion.
Which is in many cases not really noticeable according the literature.
So where open baffles really shine, is from 80-150Hz and up.
But as always, it depends of context and how you compare stuff.
If you would just compare a open baffle or dipole direct to something like a standard 3-way system, the definitely have the benefits of dealing with the room much better. Another flavor of this is the cardioid.
From a construction point of view, open baffles are a lot easier to make.
And to some extend, this is maybe also the psychological power of the system.
It's kind of magical to hear such (great) sound just from a wooden panel or board.