Latent capacity is one aspect of scalability where you include additional performance and availability resources into your system so the system can easily handle unusual peak loads. You can also monitor how latent capacity is used in a deployed system to help determine when to scale the system by adding resources. Latent capacity is one way to build safety into your design.
Analysis of use cases can help identify the scenarios that can create unusual peak loads. Use this analysis of unusual peak loads plus a factor to cover unexpected growth to design latent capacity that builds safety into your system.
Your system design should be able to handle projected capacity for a reasonable time, generally the first 6 to 12 months of operation. Maintenance cycles can be used to add resources or increase capacity as needed. Ideally, you should be able to schedule upgrades to the system on a regular basis, but predicting needed increases in capacity is often difficult. Rely on careful monitoring of your resources as well as business projections to determine when to upgrade a system.
If you plan to implement your solution in incremental phases, you might schedule increasing the capacity of the system to coincide with other improvements scheduled for each incremental phase.