FTL is a big plot shortcut, of course, since even light takes years to get from star to star. But even when Our Heroes go from planet to planet in the same system, it doesn't take long. Hours maybe.. or whatever the script demands it to be for dramatic purposes. But in reality, planets are far apart. Our fastest probes take years to get from one place to another. Heck, the Moon is our closest neighbor in the entire Universe and it's still three days flight away. Of course, in the future we'll have faster rockets and all that, but still. Unless your whole plot revolve around some slower-than-light ship taking decades or centuries to get to the next star over, you have to use FTL. Without it, you'd have a vvvverrrrrryyyyy looooooooong movie with nothing happening. After all, space is big. That's why we call it that.
Things are far apart in space. If you took your spaceship through the asteroid belt, you wouldn't even see an asteroid unless you really knew where you were looking. There's very little reason for ships to stay really close together, like the fleet in Battlestar Galactica. And if there were battles, you'd expect the combatants to stay as far apart as possible, and whichever ship had the longer-range weapons would have a huge advantage. But they would look really tiny on a TV screen.
If you do manage to travel close to the speed of light, the time dilation effects should be huge, says Kakalios. To the point where a few days traveling at light speed should mean that hundreds of years for the rest of the universe. When DC Comics had Supergirl appear in the 31st century in Supergirl and the Legion of Super-Heroes, and everybody was asking how Supergirl had traveled forward in time 1000 years, Kakalios actually emailed writer Mark Waid, suggesting that Supergirl could have been chasing a Dominator at light speed for a few days. That, by itself, would cause 1,000 years to pass. Waid responded that that was way better than what he'd come up with on his own, which was a rogue Zeta beam. This is something that science fiction stories "have to get wrong," says Kakalios, "unless you specifically wanted to fold time travel into the future into your story." And if you go backwards to your destination at light speed, it's not like the odometer rolls backwards — you just go further forward in time. Image by Layne Johnson via Concept Ships