We could do it until about 1970. Wonderful smell and such fun for a firebug kid like me.
Most incorporated areas don't allow it anymore because it contributes to violations of the NAAQS (National Ambient Air Quality Standards). Violations impact Federal funding in a serious way. The criteria pollutants from leaf burning are carbon monoxide and particulates (I'm guessing). In some places it's also a major wildfire threat.
I work in air quality (I'm such a geek) but I miss the smell and the sight myself.
Belated welcome....we NEEd more "geeks" here, especially those who work in "air quality"..the amount of "hot air" generated, and "smoke being blown up a******s is truly astonishing..(G)