The reason why this song cannot be used indiscriminately is because of copyright.

Song copyright is one of the intellectual property rights of music creators. It is the right that songwriters enjoy over their creative works. The copyright of the song "Saye" belongs to the company and individuals. Unauthorized use of the song may constitute infringement and involve legal issues. Specifically, if a company or individual wants to use the song "Saye" as a soundtrack for advertisements, product promotions, or TV series, it needs to obtain authorization from the song copyright owner.