Well... You don't actually NEED a premium chef's knife. No more than anyone NEEDS a Ferrari or BMW to get to work and back. But I'm guessing you WANT one. And the underlying principle is the same as any other luxury: performance.
Just as a sub-compact car will get you from A to B fast enough, a cheap stamped-out knife at the supermarket will still cut food. But it won't do it with as much precision or style as a good knife.
There's a long list of reasons to get a top quality knife for your kitchen. Any of the following appeal to you?
Quality knives have carefully designed blades and handles for the job at hand. More ergonomic handles, bolsters and finger-guards make a good knife easier to use, safer, and more comfortable.
The blade will be better balanced, carefully constructed for the best cutting experience. And if this sounds a little strange, talking about the "cutting experience" or "performance," then I challenge you to try a really good knife. The comparison is like comparing a modern cellphone with an old rotary phone. They're completely different machines.
No one will agree faster than me that top quality knives cost top dollar. They are typically in excess of $100, even $200 dollars. At the same time, however, they are a lifetime investment. A cheap knife from the dollar store is likely to break, chip, and lose its edge after cutting a banana. A good knife is a lifetime investment. They hold their edges longer, don't wear down or dull, and are more resistant to the regular wear and tear.
Which doesn't mean that a great knife is maintenance free. They still require care and attention to maintain their peak sharpness, but we are far more likely to value something that cost us a pretty penny. A premium kitchen knife demands respect and care, resulting in a longer-lasting utensil.
Besides some of the obvious features - strength, sharpness and weight - the quality of steel used to make a knife contributes to other quality control issues. Did you know that some kinds of steel can change the flavor of your food? Or that certain trace metals increase a knife's hardness, flexibility, and ability to take an edge?
There's also the look (and some function to go with the form) of the metal. Some knives use a lovely Damascus steel to sheath a harder but more brittle cutting core. The resulting blade is covered with a misty appearance that is quite striking.
And we return to the obvious. A better knife is sharper for longer, giving the discerning chef the ability to make finer, straighter, easier cuts. And a sharp knife is a safe knife. It doesn't slip, needs less force to cut, and it's surgical edge commands respect and caution where a dull knife may be dangerously ignored.
So you may not NEED a really good knife for your kitchen, but you certainly WANT one. There are plenty to choose from, in numerous styles. And many reasons to get any one of those styles for your kitchen right away.