Benefits
Familiar gmail interface – Many people have used personal gmail accounts. Your Google Apps for Business account gives you the same gmail interface with your custom branded email address.
Best mobile email – Between gmail and outlook, most users prefer the mobile experience and compatibility of Google gmail.
Premium spam filtering – As the largest email provider, google sees the most spam. While this sounds like a bad thing, from an engineering perspective, this gives Google the chance to block it before other providers even know that it exists.
Deliverability – Small, medium and even large email providers (like Yahoo) occasionally get added to blacklist services. Sometimes it is the accidental email use by a customer and other times it’s a systematic problem. Between Google’s size and responsiveness to spam accounts, it is very uncommon to find them blacklisted.