There are many good reasons why a company might want to re-brand. Entrepreneurs by their nature see the benefits in upping their game. Constantly raising the bar within their category keeps the competition on edge. They spend more time keeping up or as I like to say. "following, not leading."
A common mistake you'll see all around you is companies who think re-branding is changing their logos and marketing materials. Without a doubt this may indeed happen with a re-branding, BUT it is by no means the definition of re-branding. You would want to re-brand if you are looking for positive change and growth for your company and you want to do it from a leadership position. A lot of companies look to branding when sales have fallen flat or growth has hit a wall. They are not happy with the status-quo and they have a keen desire to be stronger and to have a brand that resonates this with their current and potential customers. Sometimes the culture of a company has become tired and there's a sense of spinning their wheels. Every brand stretches and contracts over time. Perceptions of the brand miss the mark simply because there were no strategies in place to lead the brand.
An unfortunate time to re-brand is when a company is in its death throes. Due to circumstances that aid to the demise of the company, realistic finances are never available to properly address a re-branding. This is where you'll see people who think changing the logo is going to solve the problem and fool the customers into thinking the problems have corrected themselves. This is lipstick on a pig. If you hate the taste of Pepsi - is changing the logo going to make you enjoy it more? Of course not. Same goes for branding.
You re-brand because you see an opportunity to take your company to a higher level. You have the confidence to determine where your brand sits today, analyze it and determine where your leadership exists and build on that. Essentially you know what you'd like your brand to stand for - this is your chance to freshen up and build towards that end. I use a pretty extensive process to get this done. There is also plenty of information out there to at least get a fix on the direction you should take. I've had many cases where a logo change wasn't needed and this was because the logo was highly recognized and that kind of cache is hard to recover.
Be sure that you get your brand right and not build on false hopes at the risk of alienating existing customers. What ever brand you have it's a must that you be authentic. There are plenty of examples in the marketplace where companies scream great service only to slowly eat away at it. Grocery chains are good at this. In the last few years (in Canada anyway) we've had them start charging for bags that were once free, having us pack those same bags where they once had bag boys. Introducing self-checkout under the guise of speed when it's about greed. Airlines and their charging for blankets, pillows, snacks etc. when they were once free. Both these industries tout service, but are actually re-training their customers at the expense of their brands. One day you will see something come along and replace their greed models and they will be standing agape with open mouths and wondering where they dropped the ball. i.e.: Blackberry today.
Your brand has to be about them not you. If you must re-brand, do it strategically. If you desire a new logo, be sure your motives reflect your corporate culture not just because you're tired of your image. An old adage I've always used is, "the point when you tire of your own image/marketing is just the point when your clientele are beginning to notice it."