Journal usually ask the author to give the original image for publication. This is to ensure high quality image is shown in journal. If the image is placed in Word document, it will be automatically compress to lower pixel per inch (ppi). Usually around 96ppi to 220ppi. However, the publisher want the image above 300ppi.
Therefore, this is the method you can use. If you save directly, it will save to a low quality, which is 96ppi. Some publisher will reject this image. Use the step given to ensure high image quality form MATLAB Figure.