No business can successfully function without a thorough understanding of their financial situation. While a one-person start-up may be able to function for a while with little more experience than balancing a cheque-book, successful growth will soon make it abundantly clear that more qualified help is required. It doesn’t take long to discover that ‘accounting” has a lot more to offer a company than just records and reports.
There are three primary accounting functions a successful company can eventually employ. Someone has to perform the basic accounting functions. That could be a Bookkeeper, but could also be a Junior Accountant who’s likely enrolled in an accounting certification program. A company will eventually require a Controller for more sophisticated financial management or even a Chief Financial Officer (CFO) for high-level financial leadership.
Bookkeepers are those tireless recorders and processors of paperwork. They “work reactively recording what has already been done financially in the company with little or no influence on business strategy.”  They record your expenses, process your invoices, and fill out your tax returns. They are excellent documentarians of your daily business dealings, but typically have minimal formal education. “When paperwork begins to compromise your time management, job satisfaction or efficiency, it’s time to consider hiring a bookkeeper.”  This level of accounting service is easy to find on an outsourced basis.
When it’s time to hire full-time within, a Junior Accountant might be the way to go. They can perform all the same basic entry functions, but they have an eye toward expanding their role in the future as they complete their formal education. They are capable of delivering a full spectrum of reporting and can often service a company’s accounting needs through a company’s mid-sized period. By that time, the incumbent may even be supervising a full staff.
Time passes to find your company is on its way … sales are great, markets are expanding. Your ARR is consistently improving with the help of a steadily increasing employee base. Your Junior Accountant has grown to a Senior position, but your business needs have also grown. It is time for the next step, but is that step a Controller or a CFO? That really depends on your confidence in your own level of financial acumen. You have to determine whether you need more help with financial data or whether you are more in need of high-level strategy or investment counselling.
Controller vs CFO
It’s very tempting to interchange these financial positions but they have traditionally performed very different functions. “While the role of a Controller puts together all the financials and focuses on the historical transactions, the CFO works with the historical information (to use) it as a tool that enables him/her to be a strategic partner to the CEO.” [2} “Put simply, a controller looks at the past, while a CFO looks to the future to help figure out how to reach the company’s goals.”  Again, a company can outsource either of these functions on a consultancy basis to start, and hire permanently when the business can support the full-time expense.
“A controller’s job is to make sure your books are in perfect order. They analyze your accounts and make sure that everything is debited or credited accurately and that there are no mistakes when it comes to the cash inflow and outflow of your business. If you don’t have accurate numbers, you might make a bad decision. This is super important and one of the reasons this is an early hire.” 
Another title sometimes heard is “Comptroller”. While the functions are more or less interchangeable with “Controller” in North America, it is a term more commonly heard in not-for-profit and government sectors. 
“The CFO then projects what is going to happen, provides strategy for the CEO to implement, and improves profitability. This can include adjusting pricing, increasing efficiencies, identifying opportunities, and enabling the CEO to make calculated risks.” 
A CFO uses the Controller’s financial data to propel the business forward. They perform the above and beyond in-depth analysis on the profit/loss statements, providing strategies to help drive executive decisions about the future of the company. They navigate complex business maneuvers like expansions, mergers and acquisitions, using their expertise in risk management to liaise with bankers and investors (with whom they maintain a typically extensive network). A CFO will apply their understanding and interpretations of current financial and business trends to influence the goals of the company and provide the leadership to all departments enabling those goals to be achieved.
Some caution that a Controller may not be promotable to CFO due to that difference in focus , but many of today’s Controllers will present themselves admirably in that future title.  In fact, Ernst & Young predicted a shift in the CFO/Controller balance more than 10 years ago, noting that the focus of a CFO’s position would shift towards investment and external relationships, allowing the Controller to take on more challenging responsibilities such as the in-depth analysis and strategy leadership.  An ambitious and savvy Controller, adept at interpreting current business trends, can be a very effective strategic aid to a CEO.
As distinctively diverse as these accounting roles are, each level provides essential information on which a business can base its decisions as it survives and grows. How many positions a CEO needs to fill is entirely dependent on how far that CEO wants to take the company.