Typically “lean” is used to describe how to develop products. But you can also look at it from a service point of view. If you aim at delivering a world class service to your clients, it makes sense to have a very clear picture of your customer in mind. A customer is playing a vital role in service delivery, she/he needs to contribute to the process – otherwise the result won´t be as expected for both sides.
What do I mean with this? Let’s take an example: every car hire customer is rewarded a certain level of attention by the front line employee. Who wouldn’t know those customers who are very demanding and seem to be eager to get as much attention as possible? The car hire company might decide not to serve this type of customer. It could be that this means not generating revenue from e.g. VIP like customers at all. This would then allow a higher level of standardization and a would then result in a more equal share of resources and attention respectively.
Personas serve as a proxy for behaviors of real world users. You could see this a typology. So, if you create (and try to serve) too many of them, you won’t be able to a) satisfy them all well enough and b) streamline the product you build. Less is more: have ONE problem and ONE persona in mind when you are building great products.
Thinking lean = standardizing = appealing only to a few or only one persona