According to Search Engine Journal, in 2014, a survey revealed nearly 60% of US Internet users visited YouTube at least once a week.
Re-targeting represents showing ads to an audience that has completed certain actions, such as visited a website, watched a video on YouTube, subscribed to a YouTube channel, or liked a YouTube video. Re-marketing/Re-targeting is a relatively safe and compelling method since the audience/viewers have already expressed interest and been exposed to the product/brand before. It serves to better engage and relate to the audience of your choice. It is also considered one of the most important targeting options in the advertising world.
Therefore, the method can be a really effective way to re-engage with the people who already are familiar with your brand and you can keep your brand in front of people who left your site without converting. For most websites, only about 2% of web traffic converts on the first visit, so it is essential to re-target those lost leads. With re-targeting you can reach the 98% of users who didn’t convert right away on your site. Both Facebook and YouTube have strong re-targeting tools. On YouTube/Google, you can re-target your YouTube viewers with AdWords or your website visitors.
At the same time, with YouTube re-marketing lists, you can re-market to people who have previously interacted with your YouTube channel. Now, you can use these audiences with re-marketing lists for search ads (RLSA).
More insights on the subject you can find here.