While others may have more/better explanations why doing this is not advisable, my experience with doing this some time ago was that the 2 desktops and 1 laptop that were each pointing to the same files were all updating their libraries and files as changes were made by me on one pc.
The main reason that I have since used Library server to share the Master library with all my devices is that when I make a change in the "server" library it only needs to be made there to be visible in all "client" devices (after restarting either Media Server or Media Center on each client). The other reason is that I don't want to risk damage to the Master Library caused by me, others, or a bug in early builds of a new major version of Media center. I always do my user testing of each major build on client devices before feeling comfortable to install it on the server pc maintaining the Master Library. Note that I only remember one case years ago where a bug in an early build adversely affected some users libraries so my delays in moving to the new major version on the server pc are out of an abundance of caution.