Yes they are , you will note the differences when zooming in the Image. 72 dpi will get useless when scaling 200 % 300 dpi up can be scaled up with ease 200% 300% without any quality loss.

same reason why 72 dpi is of no use for printing on paper as it is already a sort of zoom in, in most cases you will zoom your Image to fit the Paper. but you will note the same result on your screen when zooming. 72 dpi is for sure not ideal to enlarge a section of the Image, fact is also that when making a professional work you usually render a larger angle so that you later can cut out a section for a better presentation but still want to have a good quality if you need to scale up the Image to fit your preference after the cut. 

so again yes the dpi is important as soon as you wish having some professional results and not just 72dpi renders for a quick web show on Instagram or Facebook. It is also to consider that some  need a good dpi  if they sell there works for prints . Artwork is not just a quick sample render that you place on the web to get a little attention in allot of cases it also needs a certain Image quality.

I always render at a minimum of 300 dpi up then I load the render in a Photo Program to adapt it, if I need it for web presentation I then reduce it to 92 or even 72 dpi but the original will always have a major quality that sure can be seen.