My dear Ruby. Growster has given me so much interesting historical info andI don't even know where to start to have a little bit of fun on this subject, so I'll just have a go as one does.
1) It can be useful when you don't want foxhunters on your land. Get your sweep to put the soot into a hessian sack that's tied on the back of a greyhound then just let it run free.
2) Soot is used in a vulcanization process to treat rubber and used in toners for laser printers and copiers. Hey, we could be millionaires next year!
3) Ruby. Just a little caveat. If someone calls to inspect your chimney please let them know you've just got the flue which, in this current crisis, will delay any further investigations until your chimney has been in quarantine for two weeks.