When you are learning an instrument - one of the first things you learn are simple melodies. Eventually you learn about scales and chords and how they interact. Improvisation is an art form when done well (think Jimi Hendrix). For the rest of us Improv can be a form of practice (rather than playing scales) - it can be a form of expression - or it can be both.
I don't usually view the acoustic guitar as a solo instrument - its more of an accompaniment type instrument in the 21st century. I've been playing my old Taylor non-stop recently. Improv for me - especially on the acoustic - is about practice - but its also about trying to play something interesting. It's something very few people ever master and something many guitarists are very uncomfortable with. Its not about trying to be Stevie Ray Vaughn - its about exploration - making your mistakes fit into the song - playing at different speeds, incorporating chromatic notes - and trying to find your own "sound" - every player has one!
Ryan Geddes is a writer, musician and entreprenuer located in Toronto Canada. When he's not writing, hes helping with House&Canvas Furniture Paint.