Salesmachine lifecycles rules:
You can create as many stages as you need
An account or a contact can only belong to one stage
If an account matches the conditions of two stages, he will belong to the rightest (strongest) one
Segments are different than stages because they allow monitoring specific groups of customers and specific behavior. A segment can be a subset of a stage. Customers can have multiples segments: e.g stuck in onboarding, NPS detractors, Upsell opportunities, etc..