My clients love it because for some people that get foils done, the roots still look way too contrasting and can look as if they are already due for another foil. This helps to soften the root so that it is less contrasting. Just make sure to ask because some blondes dont like that it adds a bit of warmth.
Also I do this in between their foil appointments. Usually I do a foil with base break then six weeks later I only do a base break then the next appointment I do foil with base break again. This helps the client because the base break makes it seem like they dont need a foil just yet and can go a bit longer.. My formulas are always specific to clients hair so I wont give that out..