Could also be useful for doing research with ebooks. Maybe show a list of bookmarks or the table of contents on one screen and the text on the other screen. Or you could compare different texts easier, showing one on one screen and one on the other. Or use one screen for notes. But I guess people that need to actually do productive research will use a desktop anyways.

You don’t need FTL travel or multi-generational ships really. If you get close enough to the speed of light, time dilation can make the travel time for the people on the ship be as short as you want. Only for the people that stay on earth would the spaceship appear to take generations. Getting enough energy to reach such high speeds would be the difficult part as well as accelerating quickly without crushing the travellers.