Record what a gig paid, who has been paid, and how far you drove.
Payments are recorded against a gig, so the money and the night it came from stay together.
Mileage is worked out from the venue's address. If automatic calculation is not configured on this install, the distance field still works — type it in yourself and everything downstream behaves the same.
Both payments and mileage feed the band's reports, which is where you export them for an accountant or a tax return.