The 'supergrade' petrol is better for cars on short journeys, as modern engines need to heat up, and get working efficiently.
My petrolhead friend instructed me to do this some time ago, and he's been proved right...
I think...
Regarding small garden kit, I use the same petrol, and while it is indeed a good idea to drain the tanks at the end of the season, I didn't have that much of a problem with the following season if there was some left, (£1.30 per litre..!), and made sure that the tools were kept in a dry shed at least, so no condensation/issues happened.