Campaign URLs that stay consistent — with the mistakes that quietly split your reports flagged as you type.
Why the lower-case switch is on by default. Analytics platforms treat
Email and email as two different mediums, and a space becomes
%20 in one report and a + in another. Nothing errors — your
campaign simply appears three times with a third of the traffic each, and the split is
only obvious weeks later. Pick one convention and let the tool enforce it.