Each year since I'm following Gardener's World (a BBC show for gardeners), Monty Don cuts off the leaves of his early strawberry plants once the harvest is done (in June or July). Last year I did it for the first time on my plants. This year I had the biggest harvest in 4 years. 

What is the reasoning behind the idea of cutting off the leaves? 
Was this (one of) the reason(s) my harvest was outstanding this year?