Each individual YouTube video can be optimised for maximum marketing effect and can concentrate on your chosen keyword phrases.
This is similar to optimising each page on your website for the search engines. Remember that Google owns YouTube and that YouTube is the second most widely used search engine. It is important to realise that YouTube is a search engine!
Each YouTube video can has an associated title, description and tags. These three elements can be optimised for maximum visibility so that when somebody searches within YouTube, your video has more chance of showing up in a higher position than the videos posted by your competitors.
In the same way that there is a right way and a wrong way for optimising website pages, there is a right and wrong way to promote videos on YouTube.