Multiple systems to interface for a task in the company (example: to sell an item your POS must communicate with the inventory software, then to accounting, then to service, etc).
When a task must bring information from several external services.
When you have to deal with multiple APIs.
Not recommended for:
Data transformation (although Talend has a software for that that works with Talend ESB)
Hands down, Mule is more cost-effective than Informatica, either on-prem or cloud, and the value only goes up form there. Reusability and ease of creation makes in-house training simple and the end result is we leverage Mule for much more than what we initially considered it for. Having used Oracle and TIBCO before as well, I find they are the tools of yesterday, not able to keep up in terms of functionality or price. Jitterbit would be a more relevant comparison, but Mule won out in the bake-off we did between them.