In Laserfiche too, the main purpose of checking a document out is to prevent others from modifying it until you check it back in (or undo the checkout).  The only difference between checking it out and getting a normal write lock is that the check out persists across user sessions, i.e. you can log out and maintain a checkout.  In most cases, if you are editing a document component other than the electronic document - moving pages, annotating pages, updating metadata - the assumption is that you will complete this work during your current session and so the client application will acquire a session lock for you rather than checking it out.  That leaves edoc modifications as the only frequently long-lived operation, for which checking it out is the correct default behavior.  So when you check out a document, we assume that's what you want to do, and so the download starts in a single operation since you would need to make local copies and upload when you are done.

So I'm not sure where the software's assumptions go wrong.  Do your users make other types of changes to a document over a long period of time?  Are they aware that normal editing involves locking too, so that explicit checkouts are not required?