I'm going to use the contactless checkout in order to skip the line at the normal ones.
No one else is using the checkout?
It is empty, except for me
As long as you are not cutting in front of everyone else, you can use the checkout. Sometimes, people do not like to checkout on their own.
I'm doing it for future people
It's good that you are willing to use the newer technologies. Maybe someone will see you using it and also do so making the lines shorter for the people who need assistance.