Here is a link explaining the origin of DST. It was thought to conserve energy, although it's efficacy is questionable. Unfortunately, the article doesn't talk about this, just the history of it.
I seem to remember British Summertime was introduced in WWII to get people out of pubs and ready for work or something. I don't really understand it but during world war II we had Double summer time where (for some reason) we were two hours ahead. And apparently there are still regular arguments about BST House of Commons*.
* robin Williams described the house of Commons as "like Congress, but with a two drink minimum"... funny but kinda unfair (I hope)
It was used to save energy. Farmers were vehemently opposed to the change. There's a lot of misinformation about it out there (and in this thread). Just read the link I provided. Since your question seems answered, I'm gonna lock this