Because there are numerous studies showing how "retirement" in the form of sitting around doing nothing shortens the length and quality of your remaining years.
Positive in general. Just two annoyances. First not being to able put the task bar on the side any longer and second (more annoying) not being able to drag a document into an app that's running on the taskbar and open it.
Maintain low muscle mass? Er no strength training has many benefits including helping to maintain bone mass but also losing muscle mass as we age leads to feebleness and all the negative consequences of that. That doesn't mean pumping iron and taking steroids but just maintaining a decent level of strength.
It's basic research and has no immediate application for normal life if this is what you are wondering about.
For astronomy, it is giving us a completely new way of observing the universe. Most other ways were based on different ways of observing electromagnetic radiation.
Primarily it means there are more potential events to observe, which again leads to better statistics and hopefully more of the interesting events.
Better statistics can help guide us towards a viable theory of quantum gravity, as well as improve our understand of what happens around black holes and neutron stars.
I'm not a scientist but: I believe it provides access to the only real "data" on events that actually occurred very large distances away. This data is valuable in aiding our understanding of the early universe e.g. the big bang theory.
