For those of you have not watched the video of how a piper's plaid is put on, I've done some screen caps from the video and labelled them to show the critical structural role of the epaulet. Video is same as linked above (https://www.youtube.com/watch?v=3ytc6LqWyms). As you'll see, the epaulets actually do more than just keeping the plaid from falling off the shoulder, so it's not just a matter of adding a tie to secure the plaid if you're wearing a jacket without ginormous, stiff epaulets. The epaulets serve a structural function that is integral to how the plaid is put on - and, if you've never seen how a piper's plaid is put on, the process is not at all obvious just from looking at someone wearing a piper's plaid!