there are a lot of books on historical performance practice that can help understand these things- here's a few:
Brown, C.: Classical and Romantic Performance Practice 1750-1900 Oxford—New York: OUP, 1999
Eigeldinger, J-J.: Chopin: pianist and teacher as seen by his pupils Cambridge: CUP, 1986
Hudson, R.: Stolen Time: the history of tempo rubato Oxford: Clarendon, 1994
Lawson, C. and Stowell, R.: The Historical Performance of Music: An Introduction. Cambridge: CUP, 1999
Neumann, F.: Performance Practices of the 17th and 18th Centuries New York: Schirmer, 1993
Newman, William, S.: Beethoven on Beethoven: playing his piano music his way New York: Norton, 1988
Rosenblum, S.: Performance Practices in Classic Piano Music: Their Principles and Applications Bloomington: Indiana UP, 1988