Companies grow as years go by, but is the logo aging with it? I'm not saying that every company logo needs a complete overhaul but there are simple changes that can be made to keep up with the generations as they come. Even the well-known Skittles company has done a redesign of their logo. Some might not notice, but there are simple factors of the logo that have changed a few times within the overall brand to keep up with the generations. In fact, they have changed their logo 8 times since the company started. Something simple as creating an outline to the name or how it is now, a simple bevel to the name/font. It's a good idea to keep a logo fresh as a company grows.
There is also the possibility that a logo needs some additional updates. That is almost a vague term because there are different directions you could go with that as well. You can keep the key points of a logo like an icon and update a font, or adjustments to an existing logo because the design ratios were not put in place originally, or even update an icon with the same concept.
Needing a complete overhaul of a brand? This would be a complete redesign. Where all aspects of the original logo you just don't like at all. This means keeping the company name but changing the overall look and design. Which can be beneficial to gathering further clients/audiences. Especially if the logo is crowded or too complex as I have noticed with older logos. Simplicity is sometimes better, because it enhances recognition, and communicates a clear and lasting message, without overwhelming the viewer.
Whichever fresh look you are looking for it's a good idea to keep these aspects in mind as your company grows as so do the generations.