The term was originally conceived by my good friend and plein air artist supreme, Weyers du Toit, initially as a comment against the uber-perfection, photo-realism or laser-cut precision of much contemporary art. While acknowledging the skill and artistry that such work clearly requires, nevertheless our opinion is that art is, by the very nature of it being produced by humans with all our subjectiveness, foibles and "mistakes", imperfect. With blemishes, scratches, wavy lines, drips, drops, dents.
That is such a large component of the joy in and beauty of human-created work, in my opinion: I love to see the marks of the maker in the piece, like the first time you see the chisel marks in a piece of masonry thousands of years old and, especially if you have worked in the medium and with those tools, can feel the strokes that made the piece. It's a three-dimensional memory with temporal displacement taking one back to the moment of making.
Imperfectionism is not about shoddy work or poor execution - it is not a comment on quality of the craftsmanship and artistry. It expects the self-discipline of the true artist to work with integrity. It is more a reflection on the humanity of art and its necessary role in our imperfect lives, than anything else.