This week, Avis Budget, the rental car giant, announced it is buying Zipcar, the largest car sharing service in the U.S. There are obvious benefits to both companies: Zipcar gets capital and more footprint; Avis gets expansion into a rapidly growing and youth-oriented market. It’s a classic move of an incumbent in a low-growth industry acquiring a disruptor who’s been successful enough to prove their worth. I’ve been a Zipcar fan for a long time (I’ve written about them here at HBR and in my book), so I hope this works out well for the company, but I see some major potential pitfalls as well.