So you optimized some code, cool! - How certain are you that you didn't introduce a bug? - Is it also running faster on this exotic platform that we still need

So you optimized some code, cool! - How certain are you that you didn't introduce a bug? - Is it also running faster on this exotic platform that we still need to support? - Did it involve API changes? - Do we need to put this into production now, or wait for the next optimization to save some time? - How much time did we spend on this? Was there something else that would have made a bigger impact? In theory you can improve things without drawbacks, but in practice you always have to make the right trade-offs.