Atester who can't report bugs well is like a refrigerator light that's only on when the door is closed. The situation may be illuminated very well—just not so that it matters. You are an information service, but to be effective you have to do more than fill out report templates and assume they are fully understood. Learn how to write and present your test results so that they get results. We call this "bug advocacy."
Bug reports are the primary work product of most testers. These documents mold your readers' perception of you. The better your reports, the better your reputation.
Programmers rely on your reports for vital information. Good reporting of good bugs earns you a good reputation. Weak reporting generates extra (and in their opinion unnecessary) work for the programmers. If you waste enough of their time, they'll want to avoid you and your work.
Programmers aren't your only audience. Managers and executives sometimes read bug reports. Personnel-management issues catch their attention quickly and grate on their nerves. Reports that seem blaming, petty in tone, poorly explained, or inadequately researched or suggest that you're blowing small issues out of proportion will create a negative impression in the minds of the people who approve your raises and promotions.
Everyone benefits if you take the time to research and write your reports well.
Any bug report ...