Bakster
If I make it that far shall ponder.
One of the key features of Science Fiction is the "science" :-)
And, sometimes that's tricky.
There's valid reasons to not include Time Dialation due to Relativity in fiction. Mostly, because it's "messy."
At 0.75C 6.67 years of "flight time" spans 10 years "on the ground." At 0.9C, 22 weeks "flying" is an entire year "groundside."
This only gets worse at supra-light speeds. Technically speaking, a single "5 year mission" of the NCC-1701 Enterprise, ought see Star Fleet Headquarters age fifty or more years.
At face value, that ought to be very handy for serial tv show runners. They would never need to have "returning" characters at ground-based HQ facilities. (And, for my 2¢, it wuld give the shows a good reason to hire older actors, too.)