The more mission critical, the more customers will expect [and potentially come back to you for compensation over] limited downtime but these days any site can find its self out of the spotlight and gone just because of a short outage.
It's not just a matter of protecting yourself, you need to be able to sell your ability to perform to get business in the first place. People have many, many options in and out of the cloud and reliability is among the top factors that make a sale, or break a reputation.
That said, no document insures you won't ending up in court if you lose someone's data or disrupt their service. Even if you ultimately win, there's a cost of fighting the battle to consider so pursuing insurance and of course investing in a more robust solution is definitely important. When you're new you want to be great but don't be afraid to set expectations too... you're not going to offer "five-nines" reliability on day one, so say that.