Why it matters
When a buyer takes over a domain, the A record decides where the website loads. Point it at the new host and the site changes over. Many aftermarket landers use an A record or name servers to show a for-sale page. A common mistake is leaving an old A record in place after a sale. Visitors then reach the previous owner's server. A records hold IPv4 only. IPv6 uses a separate AAAA record.
Source: cloudflare.com