I found this activity quite easy as this is what I do at work everyday.
We will typically ask for our clients to provide 5mm minimum of bleed on their artwork before we are able to print and we will ask that they remove any crop marks as we will add those onto the document when printing. We will also ask that they provide us with a 4mm border of clear space around any artwork/file so that the trimming process is made easier and none of the important information if trimmed off.
When saving the file as a pdf we will go down to marks and bleed and adjust the bleed from the document settings, which is 0mm to 5mm to all sides of the document. If the background it just plain white then the bleed isn’t compulsory as we can just add a gutter which spreads the artwork apart, leaving a clear white edge, but bleed is always appreciated (:
Bleed is very important to include as without it, part of the document/ artwork could be cut off and it could be some of the most important information.