I've noticed that many times people try to incorporate too much into a logo; cramming three different icons into one. However, doing so ignores the true purpose of a logo. Logos should be kept clean and simple in order to be recognizable, timeless, and versatile.
Good logos are recognizable.
You want your logo to stand by itself. McDonald's, Apple, and Nike all have recognizable logos and they achieve this by creating simple yet distinct shapes. These shapes are easy to remember and make an impression when you see them. A complex logo is difficult to remember and therefore difficult to recognize when you see it again.
Good logos are timeless.
Whether it's because of changes in scope of work, marketing, or product design, businesses evolve as they mature. This often happens in order to follow trends and adjust to the times. Though some logos may be tweaked slightly as the brand progresses, these changes should be kept minimal. Making drastic changes to a logo is like changing your name from Bill to Sue, it's confusing to anyone who knew you as Bill.
The Starbucks logo is a great example of a simple logo that has been effectively tweaked as the brand progresses. The simple circular shape, sans-serif font, and mermaid character has allowed Starbucks to keep the same assets within their logo. They are able to progress with the times while maintaining a recognizable brand through slight changes including resizing their mermaid character and removing text.
The Nike logo is a great example of a clean logo that remains timeless without any modifications. Created in 1971, it still looks contemporary and will probably look that way for another 50 years.
Good logos are versatile.
When designing a logo, it's easy to get fixated on its aesthetics, that you forget about its application. Logos are placed on different products, mediums, textures, and colors, and will be featured in many different sizes. Often times a sponsor or partner will use your logo and you will not have the ability to choose how or where it is placed. Therefore, your logo should be simple so that it looks appropriate in many different settings. It must be legible at small sizes and able to be printed in monochrome. By keeping your logo simple and clean, it allows your products and website to have more complexities without your logo getting in the way.
It's easy to overdo a logo, especially when it's meant to encompass a brand's image and values. However, there should be as much emphasis placed on functionality and practicality as there is placed on symbolism and aesthetics. A clean and simple logo is almost always recognizable, timeless, and versatile.