Docker Vs Virtualization. (Advantages, startime and use cases).

Please refer below figures - 

Basic Virtualization - 

In Virtualization, to launch each & every app a hyper visor and Guest OS layer is required which makes the overall system very heavy and hence, more resource allocations. 

Docker -  

Whereas in docker, these layers are removed and directly the apps can be launched (in individual containers) True, the same goal is achieved with less resource consumption.