The loss of information. If the project information is stored in different places or the information was given only in oral form, it leads to data loss, inconvenient use (everybody knows that the information is present, but only a few persons know how to use it and where it is placed). As a conclusion, the information must to be stored in one place.
Tracking the status of the product. The developers can see the uncorrected errors and appreciate the amount of coming work. Testers monitor the status of bugs; check the corrected bugs in the new version of the product.
Project managers use the bug tracker for analysis. Using bug Tracking System project it is easier for project manager to answer the typical questions of customer/ company managers: "When the product will be ready?", "How many tasks are open?" and "When the release can be planed?".
In the next article I will consider the most important points on the formulation of defects. This is a very important point. The most testers, who are beginners in this work, pay this point too little attention. However, it is a mistake :)