Logo mockup templates are layered PSD files that are editable . And are a great way to represent your design to your client. It is best that client gets a visual on how the logo will look when printed. Since Logo iteself is a visual representation of a brand and the client is already expecting a Visual outcome from your side , a logo mockup rightly created increases a chance of being approved.
The best Logo Mockup file should be realistic , well layered and easy to use even for a novice graphic designer. I have complied a list of Free Logo Mockup PSDs that i found very useful. hope this helps you get some projects finalized.