Usually people think that by setting the attribute "immediate" true, bypasses the validation life cycle but this is not true in every case. If you talk about CommandButton and CommandLink, then its true and after "Apply Request Values" phase, request processing cycle shifts to "Render Response" phase thus skipping "Process Validation","Update Model Values", and "Invoke Application". ActionListener and action method associcated with CommandButton / CommandLink is executed in "Apply Request Values".
When we talk about editableValueHolder like InputText, and other controls, setting immediate "true" does not bypass the validation or other phases. Infact it just prioritize the control for validation e.g. if you want to validate one input control first than others, then you can set "immediate" for that control to "true".