Does staying in key matter?

Does it matter what key your song is in?

So that's one answer: It doesn't matter if you don't know the key of your song; you can still come up with progressions that sound great.

Do key signatures matter?

Key signatures mostly matter if you have to accomodate singers and instruments with a limited range. They have no intrinsic meaning. That said, leaving your comfort zone is generally considered a good idea. If you stick to one key, you may stick to what feels comfortable in that key.

How important is key in music?

The key usually identifies the tonic note and/or chord: the note and/or major or minor triad that represents the final point of rest for a piece, or the focal point of a section.

Do songs usually stay in the same key?

Some songs stay in the same key all the way through, and some songs change keys. Or it could start in C major but incorporate chords borrowed from other keys, use melody notes outside of the notes in the C major scale, or it could leave the key of C major entirely at one point, only to return to C major before it ends.