Any recent examples in the $100 Million plus arena?
(And yes, a bootstrapped business worth over $100MM is probably generating a meaningful profit, but the founders may not be comfortable reinvesting it.)
Microsoft took a small mezzanine round right before they went public. They didn't need the cash, but it brought investment bankers on board so that they had an incentive to get the best possible price in the IPO. Similar story with Whatsapp; they didn't need the cash, but having Sequoia on board gave them a stamp of approval that probably helped their negotiating leverage both in attracting employees and in selling to Facebook.