Tracing a bitmap image creates a vector copy that closely resembles the original image. When using a simple bitmap image, it is often easier and less space consuming to trace it and then edit the vector tracing.
Vector drawings use less disk space and memory than bitmaps. Since drawing files containing bitmaps can be quite large, converting bitmap images to vector drawings saves disk space.
You can create interesting visual effects by tracing. For example, with a little experimentation, you can create stylized graphics or drawings that look like etchings.