The Laser Interferometer Space Antenna (LISA) will provide the largest
observational sample of (interacting) double white dwarf binaries, whose
evolution is driven by radiation reaction and other effects, such as tides and
mass transfer. We show that, depending on the actual physical parameters of a
source, LISA will be able to provide very different quality of information: for
some systems LISA can test unambiguously the physical processes driving the
binary evolution, for others it can simply detect a binary without allowing us
to untangle the source parameters and therefore shed light on the physics at
work. We also highlight that simultaneous surveys with GAIA and/or optical
telescopes that are and will become available can radically improve the quality
of the information that can be obtained.Comment: accepted for publication in ApJLetter