I know there are a lot of reasons (and probably a bunch more I don't know) why this is totally impractical but it would be kinda funny if at some point in the future humanity wants to get a robot presence in some other star system ASAP and is like "oh, speeding up an autonomous craft to near-light-speed is too hard, let's instead find some kinda planet or asteroid or so near our target that has the right kinda materials on it and blast it with enough light ('light' in the sense of something on the EM spectrum) in the right places to create the thing we need"

conversely it would also kinda suck if earth got wiped out because some aliens wanted to have a computer around this area and their remote litography tools were a bit too coarse to be survivable

@jann Related XKCD: https://what-if.xkcd.com/13/

Also see Debate on Fermi's Paradox: https://en.wikipedia.org/wiki/Self-replicating_spacecraft

@buherator yeah it sucks how lasers don't actually output a bunch of perfectly parallel photons