The general idea is, pixels per square inch will remain the same pixels per square inch, no matter what the size.  The DPI determines that.  You can go with 72 DPI and render large, but its when it comes to printing, even print houses don't want that.  Each has their own base minimum, but most are well above that base.   The reason is because, as a printer sees it, no matter how good it looks on your monitor, its only placing ink in 72, instead of 300.

For instance, in a digital camera, you can usually set the DPI yourself.  If you take pictures at 72 or 300, they are the same "size" but look at the quality.