Depends on the spec of your S1. If it's well loaded from factory there are probably less than 5 things you can tweak, if it's poverty spec there are more like 10 or so.
Keep in mind any time it goes in to the dealership they may apply update which may revert your tweaks back to stock.
If you can find someone local that'll do any tweaks you want for £15-20 and restore them for a tenner any time you go to the dealer (that's what I offer), which isn't going to be more than once a year and even then only half the time they might do an update then owning VCDS yourself probably isn't worth it.
I've had 5 VAG cars over 4 years so was more worth owning the cable, and also have quite a few car friends, plus I get ~1 forum customer a month so it's paid for itself easily now.
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