First of all, watermarking your photos and videos will provide protection from people who might want to steal your work. Nowadays, it is easy for people to look for the images they like and it is even easier to download and use them for profit. Once the watermark is present, you will then know that one has committed a crime when they opted to use your photos and videos without your consent.
Next, watermarks on photos and videos can be a tool to popularize your work and your style. Having your information on your photos and videos will help viewers to easily remember you. And in case they become really interested in your works, it will also be easier for them to contact you if ever they want to offer partnerships or commissions.
If you are looking for tools or programs where you can add watermark, microsoft powerpoint offers a pretty simple procedure. Let me know if you need any help!