General   (General discussion, talk about anything.)

mollie, I believe that many musicians play around with music for various reasons: some play around with pieces of music just for fun, some for inspiration due to having difficulty to come up with new ideas, some to feel if they can do something with the song, some to pick up techniques.
Bands tend to play other people's songs to try and master that particular style and rhythm. These bands often choose a style which they like and which is the style they wish to adopt.

The analysis of this area is deep and wide.

With regard to Beethoven's 'Für Elise', it is possibly given to a music student/pupil as a progression from 4/4 time scale - introduction of a new (for the student/pupil) time scale - and this is why some music students/pupils may first face difficulty. It is considered that the 4/4 beat is a natural rhythm to many cultures and it has certainly been used often in beat music and rock music. The sudden introduction of a different time scale (3/8) may be difficult to immediately adjust to.
The same can be said of the time scale (3/4) which Johann Strauss (Strauß) used for his composition 'An der schönen, blauen Donau' (The Blue Danube) and which is another piece of music commonly given to students/pupils wishing to learn the piano.

Are these pieces of music difficult to play? A pianist only needs to adjust to the different time scale and maintain that time scale (rhythm/beat et al) to feel both comfortable and at ease with the piece of music.