I do if the client requests one, usually for logo usage. This is generally info re. colouration, minimum space around logo, instructions NOT to scale out of proportion, info re. setting on a background colour or background image etc.
Sometimes you may need to provide information re. the use of an accompanying typeface should the brand require flexible straplines to sit alongside the logo.
I usually set them at A4 and save as PDF rather than providing an actual physical document.
As packaging graphics are my thing, I often create a layout of a typical pack/component and use 'X's or blocks to show the layout of elements in relation to each other.
Most of the time guidelines aren't required as 99% of the time you the designer is using the logo/identity to create the poster/carton and hopefully you know your own rules!