What is the big deal?

I apologize that most of this is vague. A question arose at work about the design of a particular piece of equipment. This piece of equipment failed and now needed to be repaired. Timing is of the essence, the shop could get it back to us faster if we just made one small modification to the equipment design. As you well know, most process equipment is designed with safeguards and overbuild for future expansion. This one had a unique design of tubes that allowed increased flow for the same diameter. So the repair shop suggested that we could save some time if we just eliminated this "weird" design. No big deal, right? Wrong, the change would have resulted in a loss of capacity of 20%!!! This tiny thing changed the whole capability by 20%.
Lessons learned: so often we think that tiny or incremental changes won't hurt and often these changes make things easier right now, but as we look into the future, this small change could limit us forever. Do things the best way you know how, stop and fix the problem the best way you know how when you find out they are wrong, and make sure that change is for the better.
I still can't believe such a small thing is worth 20% of the total capacity!