Some cloud providers have limits on rate of instance creation: e.g. 2/second, 25/minute.
If 3 instances are specified in JClouds Instance Creation for a build, then it will fail because it will exceed the provider's limit by trying to request 3 concurrently.
Introducing a "delay between requests" (e.g. 1-10 seconds) would resolve this issue at little relative cost to the build time.
NOTE: this feature could instead be added for the Cloud Instance Template in the Configure System section of Jenkins which would fix a similar issue: if multiple concurrent builds that are attached to this label are executed at the same time causes this rate to be exceeded (I think)