It doesn't work -Then they all have to be dismantled. But now you need a NEW legacy system to account for the "old new" and "old old" processes. And need to retrain people, and establish new logistics tails, etc.
It IS difficult to go back in an organization of any size. (read our retirement rules sometime, or the numbers of "points" a reservist can acquire in a given year over their career, or whether SMP time counts, or our arcane pay & allowances system, etc.)
NOTE: This is not a "fear of change" perspective. My civilian job is all about change (Literally, the PURPOSE of my job is to introduce new things and change old ones), as was my time as a BN CDR. It is about being intelligent about change and understanding WHY the current system does things the way it does. Maybe those reasons were never thought out well in the first place, Maybe those reason are obsolete, Maybe those reasons were well thought out and still relevant. Which is the case matters. A lot.
I used to have arguments with many of the civilian workers on post and I was active when I was trying to take care of troops, I would get this statement many times when errors or unnecessary red tape was delaying things from being done, and my response was always "just because it has always been done that way doesn't mean it is right and how it is supposed to be done." I used to ruffle a lot of feathers that way and my COC used to get lots of phone calls on me, but their first response to them was, "was he disrespectful, "no", was he tactful, "yes", was he right, "that's not the point," and the convo usually ended there.
Many people who have been doing a job a long time like to use this excuse to keep from progressing and moving forward.
Keep traditions yes, but don't let a bad process go unchanged because its how it has always been done.