A logo's flexibility is extremely important. There are so many mediums in which your logo will be employed: digital, print, physical products... it's important that your logo looks great when used in each.
If your company uses a logo that solely relies on color, your logo will lose it’s effect when it’s in black and white. Similarly, if your company intends to only use your logo in a specific way (such as on a website or business cards), then size may not matter much. But if you’re like most companies, you’ll need a flexible logo that can be placed on multiple products, presentations, graphics, and websites. Versatility is important because it helps you reproduce your logo in a wide variety of ways.
The most successful logos are flexible enough that they don’t get lost when changing sizes, backgrounds, or mediums.