Understand that it is just like bleed but is restricted to non printing information like title and date. This important information is used to recognise a document. As a result, this piece of information is very vital for the vendor or the purchaser. A number of times the document is revised or edited, and this is listed in the slug. Nevertheless, it is taken out before the final version is created.
It is used for printing that goes beyond the end of the paper following the trimming of the document. The printer has to use bleed if there is some space in the document layout touching with the page border. This helps if any element makes contact with the border and therefore, gets left out before final printing is performed. Whenever you are printing a brochure, you give the printer a big piece of paper in order to cut it and come out in perfect size. Therefore, bleed allows you space for mistakes that can occur while printing like the expansion or contraction of paper, cropping machine not used the right way or if the person using the machine makes an error. Remember that bleed can be partial or full depending on the size of the paper.