Actually the Configurable options quantity slider only allows to have a quantity to start from but not to bill from.
For example, if you configure a Disk Space to start from 5GB and bill each GB 1 Euro, the customer will be invoiced 5 Euros per default.
What if I wanted to offer the first 5GB?
Will I will need to configure a coupon code, a bundle or use the dropdown list?
Which is really not a good commercial ergonomic.
Actually, I already opened a feature request but seeing how long we already asked for Multilingual products titles and descriptions I am not that optimist to see this implemented anytime soon.