The biggest thing will be that you will need a really clean starting image. You can "upscale" it to 300 dpi if you would like, but most likely it will be an artificial enlargement unless you are creating images from scratch.nick, what do you recommend the DPI be set at for 72", Is 300 ok?
So if you can get a really large, un-manipulated (not already enlarged) original image, then you can do 300 dpi and should be very happy. I find it very rare to find images that are THAT high of quality, so that is why I save the filesize and do most of my work at 150dpi. Since we are printing on fabric which already isn't as smooth as paper, let alone photo paper, there is some details that get lost. Don't get me wrong, they still look amazing, but this can work to your advantage in that it helps to hide enlargement artifacts.
When I do enlargement for people, I work to remove as much of those artifacts as possible so that they don't show up at all in the final product.
For example, I found a random Black Panther movie post image via Google. It was 24" x 36" @ 72dpi. The image looks to be full resolution (not enlarged at all) and is 1.9MB in size.
I ran it through my enlargement software with the same starting settings that I use for almost all enlargements when starting with a good source image.
At 150 dpi, when viewed at 100%, you can see that it has been enlarged... The image is softer, and the more you enlarge, the more it looks like a detailed water color. It still will be outstanding when printed. File size is now 15.2MB.
I process it at 300 dpi and change nothing else. The look of being enlarged is even more pronounced at 100% viewing. The file size is now 48.2MB.
Even with the PhotoZoom Pro software I use, I've only "faked" the pixels that are needed to make it bigger, and the benefit of "faking" above 150dpi really starts to be negligible. The other factor is that places like MyFabricDesigns have a file size limit. I've never been able to upload a file that is even close to their posted file size limit either. Keep in mind that this is still just a 24" x 36" image. Going bigger will compound those file sizes.
So yes, 300dpi would be great if you had an image that big that didn't need to be enlarged due to a great native resolution, but the limitations of file size and the diminishing benefit between you enlarging to 300dpi, or using a 150dpi image and having their printers do the final enlarging to their native 300dpi, it really doesn't look much different.