Is there a reason we're doing this instead of setting the value in the MKTG_URL_LINK_MAP to None? It seems like some of the code explicitly checks for that...? In general, I'd prefer to have configurations that override a variable later on (i.e. change the value of MKTG_URL_LINK_MAP directly), rather than looking at another setting and doing subtraction based on it. Particularly since this for loop is being done in aws.py -- if I set UNUSED_MKTG_URLS in dev.py, it wouldn't actually have any effect, right?