Let’s be honest: one can do without a guide, same as one can get a fit without the benefit of a gym or learn a language without a language teacher.
But let’s face it: few people get fit by exercising in their living room or learn a language through a book and some CDs.
It takes time, effort and discipline (not to mention a good memory) to thoroughly study a place you’ve never been before and even if you do, the experience on the ground can be quite unlike what you’ve read even in the best illustrated guide book. On top of that, unfamiliar concepts are rarely comprehended unless interpreted by someone with first-hand knowledge of them.
In short, a guide is a shortcut. He (or she, but allow me to use just the first) will save you time and effort. He will know all the facts to be found in the best guide book, plus countless others no book can contain. He will have answers for you just when you ask them, without taking time to leaf through 500 pages to look something up. He will know the best route, plus a few shortcuts the book doesn’t mention. He’ll be updated, and will know all about changes in opening hours, timetables, and so on. He will know about the strikes and other events that may upset your schedule. He can help in case of something unexpected, such as illness, flight cancellation, strike, etc.
He can advise you on how to avoid being ripped off. He can offer tips on where and what to eat, what to enjoy and what to avoid. He can tailor a tour to your needs and tastes. He can adapt, delivering a playful tour to a family with children and an fact-filled one to a group of history buffs.
Above all, your guide, if local, will be a window to the culture and mentality of the country you visit. He’s your instant fact finder to ask about anything that sparks your curiosity. He’ll tell you about the customs, habits, mores and morals of his people, and explain all the curious things that make his country different from yours.
That said, the guides of Greece are a distinct bunch, among the best educated in Europe. By law, they have to study 2,5 years in a University-level school to get a license to guide. Then they have to pass very strict exams during which they are tested on their knowledge of the entire Greek history, prehistory, archaeology, sites, geography and more. They also have to prove their proficiency in both Greek and at least one other language, the one they will be licensed to guide in. All in all, one could say they’re walking and talking encyclopedias of things Greek.
In short, although a guide is not necessary, it is worth your time and effort investing in one. Having spent a few thousand dollars for a trip to Greece, spending another hundred or two on a guide will enhance your experience of this country and will save you a lot of time and hassle.
The choice of course is entirely up to you.