For example, Amazon describes response time requirements for internal services in terms of the 99.9th percentile, even though it only affects 1 in 1,000 requests.
Something to be wary of is tp99s on the general population when you have sparse data.
Its easy to return nothing, and if you are starting a service for a feature, the data may start as sparse. Create another metric for when you are returning data and monitor that so you arent surprised as the data fills in.
