To get that close to the dwarf in the first place a planet would have to migrate from farther out in the surviving system (the red giant phase of the star would have obliterated worlds that originally formed close to the star). Any number of chaotic planetary pinball interactions in the outer system could hurtle a planet inward.
The star's tidal pull would transform the planet's orbit from elliptical to circular.
But the price is tidal heating that would bake away any water, turning the planet into a Venus-like world. The dwarf's intense ultraviolet radiation would efficiently break apart water vapor into hydrogen and oxygen.
If the migrating planet were an ice giant, like Uranus or Neptune, it might not be totally dried out. Or imagine a Titan-sized moon that may have enough of a water reservoir, and geologic mechanism for continually irrigating the surface, to survive being made bone dry. "Planets are complex objects and we hesitate to rule our habitability," say the authors.