The main reason that people use us is permissions management. We are the source of truth for which of your users can access what, and linking that to billing. Eg, we know that because user ABC is on Pro tier and bought 3 top ups, they have access to 75 AI credits. If their next payment fails, they should only have access to 15 AI credits (etc etc). Our value is in handling this matrix of scenarios related to usage resets, billing cycles, transitioning between monthly and yearly plans, etc.
Lago only handles billing, so if you're using them, then the logic to sync up the user's permissions with the billing state has to be handled yourself.