More concurrent users
The simplest problem and the one architecture solves: components are containerised with no significant local state, so adding capacity means adding instances behind a load balancer. The relational database remains the point to size carefully, as in any application.
What's useful to know during evaluation is that declared permissions introduce no post-filtering cost: ownership and visibility conditions translate into filters applied at source, not into discards performed in memory after reading more than necessary. It's a difference that shows at volume.