DNS MX Configuration

Kindly let me know the difference in configuring DNS MX. I have two setups below gmail.com and microsoft.com which has it's own DNS MX. What are the pros and cons of having DNS MX in each setup.

Setup A (One MX dedicated to one server)

gmail.com       MX preference = 5, mail exchanger = gmail-smtp-in.l.google.com
gmail.com       MX preference = 40, mail exchanger = alt4.gmail-smtp-in.l.google.com
gmail.com       MX preference = 10, mail exchanger = alt1.gmail-smtp-in.l.google.com
gmail.com       MX preference = 30, mail exchanger = alt3.gmail-smtp-in.l.google.com
gmail.com       MX preference = 20, mail exchanger = alt2.gmail-smtp-in.l.google.com
gmail-smtp-in.l.google.com      internet address = 74.125.25.27
alt4.gmail-smtp-in.l.google.com internet address = 74.125.131.26
alt1.gmail-smtp-in.l.google.com internet address = 74.125.142.27
alt3.gmail-smtp-in.l.google.com internet address = 173.194.68.26
alt2.gmail-smtp-in.l.google.com internet address = 74.125.140.27

Setup B(One MX to multiple servers)

microsoft.com   MX preference = 100, mail exchanger = mail.messaging.microsoft.com
microsoft.com   MX preference = 10, mail exchanger = microsoft-com.mail.protection.outlook.com
mail.messaging.microsoft.com    internet address = 65.55.88.22
mail.messaging.microsoft.com    internet address = 94.245.120.86
microsoft-com.mail.protection.outlook.com       internet address = 207.46.100.11
microsoft-com.mail.protection.outlook.com       internet address = 65.55.169.11

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Jayaram