Since the start of mankind, there has always been a role for the architect to construct and design buildings. Although from humble beginnings, they may not have operated in the capacity they do today. One of the first was Imhotep from the third kingdom of the Egyptians. Considered one of the first architects and engineers, he created the famous step pyramid that still exists to this day. He managed to create effectively, a long legacy of professionals effectively creating and designing buildings that went above and beyond, utilizing beauty, form and function.
By the middle of the renaissance period, the profession had been formalized and architects and designers began to create massive structures using techniques developed by the Greeks and Romans. Filippo Brunelleschi pioneered the use of linear perspective and using the same techniques as the Romans in the construction of the Parthenon, covered the huge empty space of the Duomo in Florence. Architecture would only become bigger and grander after this.
While the architects of yesteryear are a far cry from the amount of work and legislation of today's architects, the profession is relatively the same. To create space that people want to be in, space that modifies how people behave, act and respond. Sometimes, it elicits positive response, sometimes negative, but it's the fact that a building or space gets people talking. How we change a space can be as simple as rearranging the furniture or as large as building a new house from scratch.
Very easily, many of us have undertaken a home renovation on our own without an architect and usually this isn't much of a problem. Most renovations involve changing the cabinets in a kitchen and putting in a new counter top, painting existing cabinets and what not. But once you enter the realm of an addition or tearing down walls, that's when it starts to get a little hairy.
We consult architects to help us create space and visualize space. Architects are the ones who point people into the direction they're supposed to move. When you build a new home, there is a massive amount of paperwork that goes into construction, title 24 regulations and stuff that would normally cause a massive brain explosion (see visual)
So while the idea of paying an architect, engineer and contractor sounds like a daunting dip into your wallet, it saves you a lot of trouble in the long run as opposed to hiring a sole contractor. A contractor will build you something that is effectively space but with little form. An architect works in details, rather than having two sliding patio doors right next to each other, perhaps he/she came up with with a folding partition door that opens up the entire space. If you want space you want to be in, consider someone who is working in space and details.