Pros:

–Multi-book contracts should mean that the company is more invested in your career, whereas single book contracts can mean you’re with that pub on more of a trial basis.

–As you said, it’s also nice to be able to focus on writing the books instead of preparing book proposals each and every time.

Cons:

–Multi-book contracts are still no guarantee that the pub will keep you. I’ve seen authors have series canceled half-way through or things go south with the relationship. Getting out of a multi-book contract can be sticky and potentially costly for the author if they have to buy back the rest of their contract.

–Multi-book contracts usually come with “basket accounting” where you don’t earn royalties on any of the books until all of the advance for the entire set has been earned out. This means that if your first book does well, but the subsequent books don’t, you may never see royalties on any of it despite the success of that one book. There is justification for doing it this way, but it is something for writers to keep in mind.

That said, I would still try for a multi-book contract if given the opportunity because I think the pros are strong enough to make up for the potential risks. But there is a freedom to being under only a single contract as well, so if you are so fortunate as to be offered one, go for it.