In my opinion, it is often useful to take the meetings but most won't be fruititious. You are likely to gain industry knowledge especially from other startups. If you are talking to a big company and you get to a meeting with an hour+ powerpoint, you have to really reconsider whether it is a good use of your time. If the deal is really you selling your SaaS software, it is probably worth it, otherwise probably not. Definitely don't take a sharp turn and sit in startup no-man's land while considering some big new partnership that will likely never work within the scope of your current vision.