If your goal is to schedule content, you will only need 1 service for each profile that you'd like to post to, i.e. 1 service = 1 profile.
If you'd like to monitor engagement on your posts in real-time, then you may need to connect an additional service per profile. Note: this would apply for Twitter and Facebook.
Additional functionality can be added using your services allocation. For example: setting up an RSS feed to auto-post or monitoring comments on your Facebook ads will each cost 1 service.