Difference between start task and start workflow

[JobHelper]

can any one explain me what is the difference of start task and start workflow from task in work flow manager

NOTE : [This question was asked by venu gopal]

[manisha.sinha]

Hi
There are many Tasks that can be performed in a single workflow. For example we may have a command task and sessions task in series (or even in parallel) executed in the same workflow.
You may want to run one or all of them together and hence the options .

cheers
Manisha