Job titles are badges of authority. Not getting the correct job title appropriate to your position, duties, authority, and achievements can undermine your standing both inside your company and with key outsiders such as clients. Additionally, not getting the job title that you are due can hinder your pursuit of future career opportunities, both inside your current firm and as a potential outside hire by other employers. You probably will be seen unfairly as someone who actually is at a lower level of achievement than the one you have attained.
Please also see our closely related article on the matter of what job descriptions mean.
Job Title Scenarios
In one scenario, an employee gets a de facto promotion but does not get an upgrade in job title to that of the former incumbent. This may signal either a downgrade in the importance of that job, or be utilized as a not so subtle device by a company to lower the level of compensation associated with that position.