When graphic designers start with the design of a PowerPoint template, they are faced with a white page. A common way to fill it is with a faded, washed out, water mark. It might look OK on an empty page, but it will clash with any other object than a text bullet point. To be avoided.
Unless other prescribed corporate template elements that are hard to change, a water mark can be easily taken out, simply delete the graphic on the page, or cover it with a white box.