One my model pdm was only ± 2,000 ko but after a few changes, it now ±58,000 ko.
I don't have some of the reported problem with the check-in / check-out.
My others models (alomost the same size) after modifications did not grow that way....
I didn't find something on the web or documentation about the way to reduce the size of that PDM file and I'am still searching.
I try to save as new and it done nothing.
I want to know if it can make problem in the future.