But if it improves privacy, I might just enable it again. How much of a privacy improvement are we talking about here?
Not much.
The whole point is that it makes your change the same precision as your payment. So, for example, if you were to make a 1-input-2-output transaction, with one output being 0.00012700 BTC and the other output being 0.00523869 BTC, then it is fairly obvious that the latter is most likely the change output. With output rounding enabled, it would turn those two outputs in to 0.00012700 BTC and 0.00523800 BTC, which might make it somewhat less obvious which one is change. However, you still have to consider other things which will reveal which one is the change output, such as matching the address type of the input, or if you later combine that change output with other outputs.
If you really want to confuse this change identification heuristic, then there are better ways of doing it manually, such as splitting your change across multiple outputs, deliberately sending the change to a different address type from your inputs, and so on. The best way altogether is to
avoid creating change outputs at all, if possible.
So for the casual user it might provide a very small privacy improvement, but if you are serious about privacy then there are far better things you can do yourself.