Daniel M. Ingram:
Choiceless Awareness practices are practices that involve no specific focus except whatever sensations arise. They are found in many traditions.
Thus, rather than have a specific width of attention, they allow attention to do whatever it does, with some caveats.
One is still generally advised to avoid being lost in the content of thought, and rather see the sensations that make up thought. One is also advised to various degrees depending on the tradition or teacher to be actively mindful of what arises, rather than just "sitting there like an idiot," as a Zen teacher once said.
Choiceless awareness practices have the advantage of being very natural and accepting of what arises, and, as acceptance of what arises is key to practice, this is a distinct benefit.
They have the disadvantages for many of lacking the precision and focus that allows the penetration of objects to see their true nature and gain insights rather than getting lost in them, not perceiving them clearly, and related problems.