Not sure if this a serious question or not. But, I'll try to take a crack at an answer...

Have you ever seen a street performer? Street musicians often perform live in the street with an open guitar case. People toss a few coins in if they like their music. This is a "tip". If not, the audience walk bye and do not "tip" the street musician.

This same logic can hold to someone sharing digital music. If one enjoyed the digital music, like the song I shared, they could "tip" the artist digitally with BTC. But, to do so, they'd need a place to send it. Hence, why I wrote in the BTC wallet address because one can send the tip there. 

Hope that helps.