A friend had a client who purchased 1000 domains for his site. I've never even imagined buying this many - can you explain how you use them? Do they all point

A friend had a client who purchased 1000 domains for his site. I've never even imagined buying this many - can you explain how you use them? Do they all point to the same site? Is the reason simply to catch people who may mistype your real URL ie ycominator, ycombinator, ycombinates etc? I find this fascinating, as even with these thoughts in mind I could only get up to about 10-20 domains for my current project! Thanks for any insight.