It's a pull from your bank account. You give the merchant your account details and sign* an authorization and they "pull" the money from your account. Afterward you can cancel the charge without giving a reason for a few weeks, or if the charge was unauthorized for up to 2 years. The only downside compared to chargebacks is that you are not protected in case of insolvency of the merchant.**

> What are the expensive consequences you are talking about?

The system offers no security for the merchant - in fact cancelled charges cost a fee, even if the charge was completely valid.

* yes - physical signature on paper, except when paying online

** this is a topic for a full comment on it's own, but here's the gist: Under German law you can't "take back" your money from an company that has filed for bankruptcy - in fact even payments made to you before the filing might be clawed back by the administrator - which means that you will receive (and customers from insolvent airlines have received) an angry letter demanding the money back. With chargebacks this is less likely to happen as the chargeback will be paid for by the merchant's bank, not the merchant directly, but the legal situation is unclear.