I love looking at a set of thumbnails. It gives me a great feel for a wedding gallery that might be 400-500 images. I can quality control adjustments I have made to each image making sure I have achieved good colour and contrast consistency between images and get a good feel for the day.
Zooming in on high megapixel images is great fun but the images have to be strong enough to make me want to take look closer.
I think looking at images at a small size lets you see very quickly if the images are strong.
Also probably the best way to judge your improvement as a photographer is not to look at your very best images but to look at how good a whole set is from any given shoot. Great advice for brides looking for a wedding photographer is to look at a whole album or gallery of images from the same wedding.
For privacy reasons I didn’t want to put a whole set of thumbnails from a wedding so as a quick example I grabbed 55 images (taken using my Sony Zeiss 55mm lens) of images mostly taken in and around Manchester.