Music Policies is powerful database on YouTube that gives out information on what happens to a YouTube videos if it uses a certain copyrighted song. The database was implemented on December 8, 2014 and has been considered helpful for those wanting to use copyrighted music as they don't have to upload a video containing a copyrighted song just to see the caused effect.
Type's of Playback restrictions
There exists different types of restrictions
If the playback say's "Viewable Worldwide". That means any videos receiving the claim will be available around the world however the video won't be monetizable. A Matched Third Party content notification will be shown next to the video on video manager. Most cover songs of artists are Viewable Worldwide.
Blocked in one country
If the playback say's "Viewable everywhere except (One Country)". The video is blocked in that one country and that one country cannot view the video. A well known example is "Viewable everywhere except Germany" which is the result in which you use a song by a GEMA protected artists prior to October 31, 2016. Love Will Tear Us Apart by Joy Division is mostly viewable worldwide but at one time was viewable everywhere except Australia. Love is meant to last forever by John Norum is Viewable everywhere except Sweden even if you perform a cover.
Blocked in a few countries
Happens when the song you're using will get your video blocked in 2 - 50 countries. The playback will say "Viewable everywhere except for (2 - 50) countries". Most older songs would be blocked in Germany and Switzerland for GEMA protected artists during most of 2016.
Blocked in a lot of countries
Happens when the song you're using will get your video blocked in 51 - 249 countries. The playback will say "Blocked in (50 - 249) Countries. Depending on computer size, The top of the countries list may not be able to be seen if the song your using will get your video blocked in more than 170 countries. Though uncommon. Obscure artists such as Cabaret Voltaire and Fad Gadget are known for having these restrictions on most of their songs.
When is song says it's blocked on 249 countries. It cannot be used but I may be allowed to be covered. Examples are some songs by Jimi Hendrix and Bill Withers.
Usage of the song will result in your video getting muted (but viewable worldwide) or blocked entirely. The message would say "This song is not available for use in your YouTube videos. If you use this song, your video may be blocked of muted. Learn More". Examples Include Scatman John which the singles from his first album is blocked entirely due to some Scandinavian Neighbor Rivalry along with it's non singles blocked in 248 countries. The Ramones and a-ha with half songs viewable worldwide and not available for use as being part of Warner Bros which although are not GEMA protected. And some artists belonging to Sony record labels. One Direction (Columbia Records), Michael Jackson (Epic Records), and Justin Timberlake (RCA Records). Keep in mind that songs that cannot be used may be allowed to be used again which is the case for Ed Sheeran's "Castle on the Hill". Any artist can have such restrictions.
Some songs are not listed on music policies. While most of them would have a playback of being viewable worldwide and would even allow you to monetize off of the video. Prince is hardly listed on the music policies yet anyone using his songs would get copyright strikes. The Beatles also had many of their songs unlisted.