Businesses that send bills to consumers (B2C) have known for a long time that inserting stuffers or adding a message to your billing statement every month will often result in a 0-2% response rate depending on the offer. These might seem like low response rates but bill messaging & stuffers are an inexpensive way to communicate and upsell your customer base. For some reason, most businesses that send bills to other businesses (B2B) haven't caught on to this yet.
Our VP of Marketing, Mitch Rose, has a great post on this here.
The basic theory is that you're paying for the postage and the paper anyway, why not add a message? It's free, it's being read by your customer, and it may be the only communication you have with them this month. The only possible reason not to do it is because you're too busy. I could imagine someone from marketing bringing this message to the CEO of a company "I'm sorry but I'm just too busy to talk to our customers." WHAT!!!
This is the time where I would go with one of my favorite sarcastic motivational lines "Let's set the bar a little lower and we'll pass out shovels."