If you have worked on Visualforce and started playing with Lightning Component, you must have identified one important missing feature, which is standard Controller.
Lets assume a scenario, you have two Lightning Components on Account page. One Lightning Component is used to show some fields and other component is used to edit same record.
Problem 1 :
To achieve this, both Lightning components would invoke Apex method separately at the cost of performance, by issuing duplicate server calls. Below image depicts problem, where multiple Lightning component requests same content by making separate server calls.