Hi Vipin,
The Visual Web Part can be used in sand box solutions and farm solutions but there are some restrictions to sand box solutions. See https://msdn.microsoft.com/library/gg615454.aspx for which explains about the restrictions of sandbox solutions. Sometimes, this is the only option if your production environment has set these restrictions or if you need to deploy to SharePoint online.
The Visual Web Part (Farm Solution Only) can be used only in Farm solutions so it does not have these restrictions.
Prashanth