My main objection is it dramatically decreases your productivity. If building and testing takes 5-10mins (which is the case in our codebase) trying to fix a bug can take forever when you aren't exactly sure what the cause is. You don't want to try multiple fixes simultaneously because if something doesn't work you aren't sure which of the fixes (if any) might be causing the issue.

Maybe a different way to look at it is: if you could shorten the BTD loop to a minute or two, why _wouldn't_ you want that?