So it can notify you when the water has reached the set temperature or the time you set for cooking is up. Which can be handy. However, I found the BT very weak on my Anova and it would lose connection when I went into my home office a mere 25’ away, so I stopped using it. There’s actually no need for the water to be up to temperature before you put your food in, and food can sit as long as you want; half the point of sous vide is to be able to hold food at temp without overcooking. So you don’t really need the timer either.