I am preparing a document to send to print. I was asked to add bleed. Is it necessary for a no background document? The image on the design will not go all the way to the edge. Or should I add a white background layer and add the bleed to that?
Make sure you didn't confuse this:
1) Did the printer said "Add bleed if you have elements going to the edges"
2) did he said "Add bleed and make your print-ready at the size of the bleed".
For #1, you do not add bleed or trim marks. For #2, you do add bleed.
It's normal they will mention to add bleed on a printer requirement/specification sheet as a tip. As you said, if the print people didn't see your design, it's possibly just the protocol. If you don't need bleed, don't add it.
Be careful in adding bleed when you don't need it; some printers blindly shrink your layout to fit a non-bleed sheet OR will charge you for a bleed print even if you don't need it. Or worse, they'll print the trim marks and shrink your layout to fit the sheet... Horrible true story scenario that can happen especially with digital printing or online printers.
If possible simply ask the printer. Local printers usually prefer to not have trim marks and bleed when they're not necessary, especially when using digital prints. It's ok if you put them but make sure to mention it.
White is absence of color, and transparent too. So adding a background or not doesn't matter. What's important is really the dimension of your file.
You do not need the bleed for the image, but you probably are asked to have one to align the page to the rest of the designs they are putting on the plate.
So if they asked that yes, do it.
I can think of several reasons for the need of bleed on a printer's metodology.
If you do not asign a bleed you could try to align designs next to each other (A) This can imply that any misaligment can be incremental.
If you use bleed (if your design need it or not that is another issue) You have a more controlled output (B)
Your project ill be printed with other projects. This can be business cards, or it is a magazine add. Your design does not need bleed but the rest do. (C)
You have an aditional process, folding, Varnish, etc. (D)
There are many reasons to work with a bleed. It does not matter if your design needs it or not.
The only case I would not use a bleed is on a leterhead where the paper is exactly the finish size.