@JBH It'd be really, really cool? I mean, we do a lot of things for pretty much solely that reason.

Also, running a massive set of supercomputers (possibly after uploading humanity to said computers). Although, if it's just to run a bunch of simulated human brains, that's kinda just a higher-tech version of the farmland idea.

Maybe a massive set of lasers for colony ships (probably only feasible in a "something bad is coming, we gotta get out of this solar system" scenario)?

hi

@Gryphon I must admit that "really cool" is always a possibility, but it tends to give way to economics. The cost of building the blasted thing would need a small interstellar empire to afford. A supercomputing array is a great idea (there's never enough computational power - video games keep gobbling it up), but the lasers for colony ships don't make sense. The mass required to build a dysonsphere is greater than the available metals in a single solar system if you mined every planet to...

...dust (i.e., you need to import mass from other stellar systems or extrasolar systems just to build it in the first place, making powering ships entirely moot).

@JBH In some kind of post-scarcity society, economics may become less of an issue. For the "propulsion lasers" idea, it is possible to throw those laser beams to other systems, so if you already have some kind of (very expensive and/or time-consuming) method of interstellar travel, you may be able to get some use out of the thing. Not a likely scenario, but cool stories aren't usually built around likely scenarios.