Adding bleed is the way that you will be able to print on an entire sheet of paper (with no white borders).
Because the printing equipment cannot print to the edges of paper, it is usual to print the design on over sized paper and then cut it down to size (the standard oversizes are known as SRA sizes, SRA4 is a bit bigger than A4 SRA3 is a bit bigger than A3). However to cope with small inaccuracies in registration (the position of the image on the page) and with the limitations in precision of cutting equipment it is good practice to have the image larger than will be needed; hence the content 'bleeds' over the edge. Some of the image is then cut off and binned.
Another design we often receive is that of a traditional three panel double fold leaflet. The main problem that arises is a relatively simple one; the inner margins need to be twice the size of the outer ones or the content will not align with the folds.