I get lot of emails from people who want to switch back to the old Google Analytics from universal analytics. Their number 1 objection is that UA is creating tracking issues and they can't figure out how to resolve these issues.
So for example if you switch to universal analytics and you are using a third party shopping cart which is still designed for the old GA then what will happen next,.......your ecommerce tracking may either stop working or it may start producing inaccurate reports.
Lot of people are blindly switching to UA on Google's recommendation without understanding the implications of such a switch.
You need to understand that everything from event tracking, cross domain tracking to ecommerce tracking works differently in UA. So if you make a switch to UA, you then need to change majority of your tracking code like ecommerce tracking code, event tracking code etc and also make sure that it works. Google will not automatically do all these changes for you just because you are now using UA.
Moreover there is not enough support available from Google and other analytics users yet. So if something goes wrong you are pretty much on your own. Also once you completely switched to UA there is no turning back. So if you can't resolve your UA issues, you are pretty much stuck with poor to no tracking.
So what i recommend is running UA in parallel with GA as long as you can (until Google force the switch on you or until you have tested and sort out all of your UA tracking issues in advance).
EDIT: According to " Classic Google Analytics won’t go away, but all future enhancements will only be released to Universal Analytics." Source: http://dan-russell.com/2014/02/whats-next-for-google-analytics-and-google-tag-manager-qa-with-justin-cutroni-from-google/