I had quit as of Jan first this year after fore-filling my contract obligation of staying on-board for 90 days after the sale in September. Since then, I have not launched a new company *yet*, but I do host several former clients again and a few new as well using customer tailored packages based on your needs and budget. Feel free to PM me to discuss a custom quote.
As was said, it's faster and safer. The relative safety comes from the fact that if a single drive fails, you will not lose your data, as it is replicated between the two drives. This is known as RAID1. If you take really good and constant backups and don't mind reinstalling things when a drive fails, a single drive might be fine. But aside from backups, there is no added level of security in the event a drive fails.