The leaves can be added to salads and taste like cool cucumber; the pretty flowers can be frozen in an ice cube to add a splash of luxuriousness to a Pimms or just used to dress up a salad.
It does self-seed very easily which in this case could be seen as an advantage but just deadhead to remove flowers before they set seed if you don’t want a carpet of borage.
Borage is loved by bees as its flowers are so nectar rich and this makes it an excellent companion plant as it draws insects to it & the surrounding crops good next to tomatoes as helps with fertilisation!