This is about the contention ratio, and service delivery. When you have many users you can still deliver great service even if the contention ratio seems higher. There are two main factors for planning the bandwidth needed, the average data use/bandwidth use, and what max utilization is during the peak, typically 6-8pm when the highest number of users are using the network. If you are selling 100mb plans, as long as you have at least 100mb of available bandwidth during the peak times, any individual user can still burst up to the plan max. So that is 90% on a 1 gig line, or 95% on a 2 gig line. 1 gigabit a second for a month is about 325k gigabytes total. Or about 160gb per month per customer data use for 2000 customers sharing a 1 gig line with near 100% use. There are also multiple steps where the contention ratio or bandwidth use matters ranging from very local, last mile issues to international ones related to peering.
