Excessive logins can eventually compete with Apaches ability to maintain open database connections.

Looking at our API docs:
https://developer.atlassian.com/display/HOME/Atlassian+REST+API+policy#AtlassianRESTAPIpolicy-Resource/ratelimitsandpaging

We state:

Resource/rate limits and paging

Resource and rate limits, and the default and maximum sizes of paged data ARE NOT considered part of the API and may change (possibly dynamically). It is the responsibility of the client to read the road signs and obey the speed limit.

For Cloud users, excessive logins aren't visible to the admins. That being said, ideally we could allow admins the ability to define a max concurrent connection on a per account basis and/or a way to throttle inbound API calls to the Cloud instance (for example, keep the traffic from hitting 300 on an hourly basis, etc).

We're seeing cases where logins are nearly reaching the 500K mark, mainly service accounts logging in via the API.