If you want to create multiple accounts and assign them different email quantity i.e. 10,000 emails/day etc, then you will need admin panel for that.
These accounts could be of your own customers, your own colleagues or account for your different brands/businesses/websites.
This server setup with customer panel is self-sufficient for sending bulk emails without re-seller panel (admin panel) for the single user.
But if your requirements are as such that you want to share this platform with others, by creating multiple customers account or if you want to add multiple sending domains then this email server setup with the re-seller panel will be the best choice for you.
With the help of the re-seller panel, you can create multiple customer’s accounts and assign them email credits.
You can charge them based on their usage or requirements and become email marketers like MailChimp or Sendgrid.
With this reseller-panel, you can see all the create customers and update their personal details and you can provide the restriction to them.
Such as if you want to create 4 customers and assign them emails (e.g. 10k, or 100k emails for particular time i.e. 1 day or 1 Month) so that they can use your system for sending emails, and for that, you will need to login into the admin panel.
Only you will have the access of the admin panel, and from the admin panel, you can control other customers activity and set the limitation like what they can see /create/update/delete and how many emails they can send per hour/day/week/month/year, etc.
With customer panel, your customer or you can log in and send emails. You can create customers account with or without email sending limitation.
Once any customer login to into customer panel with their user credentials (which you have created from admin panel), they can perform many tasks such as they can create the contact lists, upload their contacts via import, they can create email templates and send emails campaign and check the statistics, etc.
Read more about the reseller panel as follows.