The longer version
White label means the booking site, emails, and receipts carry the club’s identity. The vendor’s name is absent or reduced to a small line in the footer. The club’s players never feel they are using someone else’s platform.
It matters because the relationship with the player belongs to the club. On a marketplace, the player is the marketplace’s user first and the club’s customer second, and the marketplace can show them a rival club 3 km away. Under the club’s own brand, that cannot happen.
White label is often confused with a custom domain. The domain is one part. The full version also covers the email sender name, receipt branding, the app icon on a phone, and the absence of vendor promotion in the player’s inbox.