All performers want to get better at what they do and gathering data on performance can help this. Gathering data is useful because:
It helps identify or confirm a problem (weakness) exists
It identifies strengths in your performance
Establishes baseline measurement criteria
Provides information with which to measure the success of implemented improvements
It can aid motivation when training
It allows you to plan targets and short/long term goals.
Data collection also acts as a good method of monitoring your progress in an activity as you can complete it at the start of a programme of work/training programme and again at the end to measure improvement