Lets say you create a video for selling one of the latest converters for video and you create a demo on you tube. Now people if they like it would have to go to the landing page of the product via the url you show in the video or any link you give in comments or description. This is like 2 steps.
But you can do it one step. What if you can add a button , a small message when people hover on the video and you can link the button to let the user check the landing page of the product, making it easier for them to buy. This way you can create a viral video for promoting your product.
Another thing you get with this is any body using the this video tag will l ink back to the link you had used in the make over. Here is an example which I have created to link to my blog feed.Just hover your mouse over subscribe button and see.