Any large organization with a dedicated IT staff can save money by having an on-premise Exchange server rather than paying a monthly fee per mailbox every month. Also, any organization that uses Outlook for the desktop email clients will enjoy the ease of setup and use. Non-Profits also have the benefit of reduced software licensing costs for Windows Server and Exchange Server but this is now a moot point with up 300 free mailboxes in O365 for qualifying non-profits. Any small startup that doesn't have the capital to invest in servers, licenses and other costs would not be well served by Exchange. Any organization, whether small or large, will need IT services, either an MSP or dedicated staff, to manage Exchange. If you do not have the staff then Exchange is not for you.