I remember Phacelia from my aunt's vegetable plot, when I was a child. I'm looking at a photo which was taken a longs time ago and is showing me standing within an ocean of blue flowers. This year I have finally grown my own.
Phacelia can be used as green manure and fits into any crop rotation plan. If left to flower, they will attract bumblebees and hoverflies, which will help, if aphids are a problem in your garden.
I can only confirm, they are brilliant cut flowers and last for days in a vase. With strong stems, lacy foliage and scented blue flowers, they suit any occasion.