To be honest, I'd like to see more therapists using the consultation card as a customer service tool - for you as a spray-tanner, that might mean asking them how their last tan worked out for them (were they happy with the colour and durability, for example) or if they'd like to try anything slightly different. If they have had problems with it fading a bit quickly (or in particular areas), for example, it gives you a chance to recommend retail products that might make it last a little longer - you make an additional retail sale, and customer goes away feeling even happier.
Similarly with beauty consultation cards, if you have done your job properly and identified any problem areas (e.g. "Last time you came, you said that your skin was really dry - how did the cream sample I gave you work?), it give you a chance to follow up and offer a continuity of care that has the client coming back time and time again. Even if another therapist treats that person, they'll have all the info to hand to offer continuity - an important consideration for managers who experience high staff turnover.