Question: why does the clocks change ?

Edward Hughes answered on 20 Jun 2014:

Because somebody decided they should. The clocks go forward in the summer time so there’s more light in the evenings (most people are awake more in the late evenings than early mornings). But there’s no physical reason for doing this, it’s just convenient!

By the way, people make similar convenient choices quite often in physics! Sometimes it’s useful to introduce something arbitrary (like the time zone) and move it forwards or backwards to make calculations easier. So your question is actually a very insightful one!