Mostly because it looks and smells nice and the bees and insects like it.
Although our local garden centre was selling bunches of lavender flowers last year at a price that made me look three times!
I'm also not a very imaginative gardener, but we had a lavender hedge before, which was lovely so I'm going for a tried and tested formula!
It was warm enough to work without jacket today, then the snow flurries came. It's nice again now, though.