Pros
The first major benefit of staying with one employer for a significant length of time is gaining expertise in the company. I have worked for the same employer for a long time, I am a senior member of my work team, and others may count on my knowledge of the company's operations to support their own efforts. I've likely earned the respect of my employer and other members of my team, and your knowledge may place you in a mentorship role for newer employee.
Cons
I want to learn new methods and systems, it can be expensive for companies to change their methods and systems for producing work, so many companies use the same processes for many years. Although this can help them streamline their methods internally, it may prevent long-term employees from learning new ways of accomplishing goals. If companies prefer not to update their systems frequently, their employees may not learn the latest software and technology that other companies in their field use.