Heuristic
Buffer variability where it is cheaper to absorb
Variability plus high utilization can create disproportionate waiting.
When it fits
- When random arrivals or service times create repeated starvation and overload.
When to avoid it
- Queueing equations have specific assumptions. Use them for directional reasoning and measurement design, not as exact forecasts for arbitrary multi-stage knowledge work.
Why it matters
Choose where spare capacity, time, inventory or flexible staffing can absorb variation at lower cost than letting the main constraint saturate. Make the buffer explicit.
An example
A critical reviewer keeps reserved recovery capacity around cutover rather than being booked to 100% while exception arrivals are highly variable.
Check your result
The buffer is placed where it reduces expensive waiting or failure more than it costs.
Keep this limit in mind
- Queueing equations have specific assumptions. Use them for directional reasoning and measurement design, not as exact forecasts for arbitrary multi-stage knowledge work.
Connected ideas
Useful withRecheck the bottleneck after improvement
Evidence and sources
Provides context
Kingman's heavy-traffic result underlies a queueing approximation in which waiting increases sharply with utilization and with variability in arrivals and service.
It is a single-server heavy-traffic approximation and should be used as directional intuition, not as an exact prediction for arbitrary multi-stage work.
The Single Server Queue in Heavy Traffic · Research note metadata and established heavy-traffic formulation