A good rule of thumb, when thinking about the final exported image using the creator: every 300 in canvas size will result in 1 inch at 300 dpi (even though the original image is only exported at 96dpi). All the online printers typically require 300 dpi- especially if you want your image be crisp. By tripling the size of your canvas, you essential "fool" all lthe online services that require 150 or 300 dpi for a final image to work with.
Triple the size of your canvas in proportion to what you want (a business card or a tshirt design for example): because of the max exported size of 2880 x 2880 the largest image you can make "at 300 dpi" is almost 10 inches square.
Why do you think the Business card templates are so huge in size? They print up crisp and clean with any online service.