Because it'd probably be better for you at the end of your journey if everyone you ever knew hadn't died of old age, including your great grand relatives. If you just want to go to the future, you can do that. But if you'd like to travel large distances at great speed without losing everyone you care about, then warp will help with that because you will age at the same rate as those you've left behind, and everything will be as expected when you return.

> and everything will be as expected when you return

Either what I said is completely wrong, or this is completely wrong. I think it is the latter.

You experiencing time dilation doesn’t make it so when you get to your destination, people have aged more. It makes it so you have aged less. If the round trip takes 2 years from the perspective of an external stationary observer, because it is a round trip of like, 0.9 light years in both directions, Then by the time you get back, people have aged 2 years. Removing the time dilation in the ship just makes is so the people on the ship also aged 2 years instead of less than that.

That’s not really helpful.

Unless you can go faster than c, you can’t go 50 light years away and come back to people having aged less than 100 years. If you did, you would have gone faster than c. Basically by definition of speed?

But for distances travelled within the Solar System, and many trips taken, it would be advantageous if traveling 0.7c because conventional propulsion will have time dilation occur at those speeds, and the effect is cumulative. Who cares for a 5 hour trip to Jupiter's moons, or wherever, but if you're spending all your time traveling around the Solar System and back to Earth with conventional propulsion at 0.7c, you'll hardly age, and everyone will get old around you. So again, warp is great for sublight relativistic travel within the Solar System.

Assuming you aren’t communicating with those not on the ship while in the ship, the only difference with warpfield is that the trips take longer for you? (Your trips take same amount of time for others)

If you go to Europa and then head back, Joe here on earth will have aged the same amount by the time you get back. The only difference is whether you aged the same amount as Joe, or less than Joe did.

The warp bubble doesn’t make you miss any more of Joe’s life. It just changes what ages you are when you experience the parts of Joe’s life that you do. (Specifically, warp bubble makes you age more quickly, same rate as Joe)