ddepth parameter of the Laplacian filter

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Here how I used to implement the Laplacian filter over my images:

 int scale = 1;
 int delta = 0;
 int ddepth = CV_16S;
 int kernel_size = 3;
 Mat res,imgGrayScale, imgGrayScaleGaussianBlurred;
 cv::cvtColor(sourceImage, imgGrayScale, CV_RGB2GRAY);
 imwrite("Im3downsampledimgGrayScale.png",imgGrayScale);
 GaussianBlur( imgGrayScale, imgGrayScaleGaussianBlurred, Size(3,3), 0, 0, BORDER_DEFAULT );
 imwrite("Im3downsampledimgBlurred.png",imgGrayScaleGaussianBlurred);
 //Laplace
 Laplacian( imgGrayScale, res, ddepth, kernel_size, scale, delta, BORDER_DEFAULT );
 convertScaleAbs( res, result);

Can someone clarify what it does the "ddepth" parameter? Why it states in the documentation that should be CV_16S to avoid overflow? What does it mean this?

ddepth: Depth of the destination image. Since our input is CV_8U we define ddepth = CV_16S to avoid overflow