"Stay In Touch" eamail campaigns are useful for all prospects that are not immediately ready to engage with sales. They form the backbone of your lead nurturing program by "dripping' out relevant content to prospects over time, helping to educate them and build trust and credibility for your company. By touching prospects regularly, they help keep your brand top of mind so that the prospect will contact you when they are ready to move to the next step.
A good place to start is with the "Buying Committee" -- the group of individuals that will be involved in the purchasing decision. Even at medium size companies (100 - 500 employees) research shows the average number of people involved in a decision is 6.8 -- and the number goes as high as 21 individuals on a buying committee at larger companies. Your nurturing content will need to to speak to each of them and address their unique needs.
Most of the people that you speak to at a company will fall under categories related to your marketing efforts, whether they have final say in the purchase or not. The category definitions may include the "Champion," a user with purchasing authority; the influencer, a person without the buying authority but with significant input, such as a consultant or middle manager or user; and the executive staff.
People want to do business with people. We're human, and we crave interaction with people who know us. When you build content especially for your buyer personas, you build a relationship with people before you've even met them.