Say I have a trace running across a board. It's 50 mils the majority of its length, but in one short place it narrows to 25 mils to make it through a tight area. As best I can tell, this will be preferable to a 25 mil trace the same length, and only slightly inferior to a 50 mil trace without the few percent of its length narrowed to 25 mils.
Is there any disadvantage to the narrowing? Odd high-frequency effects? EMI? Obviously traces have many possible uses, including delivering power, carrying signals of different frequencies, grounding... so under what circumstances will this matter?