I have also been told that there is no physical reason to wait, and the advice is given to help dating. This is not just for the sake of easing doctors lives though.
There are some very rare conditions that may go unidentified and result in serious health problems and a long delay in the time it takes for a woman to be able to conceive again.
I had a suspected partial molar pregnancy, in the end it turned out not to be molar, thank god, but for a while after my miscarriage I was looking at some very serious treatment (chemotherapy for minimum of 6 months and then a years wait before tcc)
Very rare conditions like molar might be identified if a woman fails to have a period, so if you wait for one cycle at least you know your body has healed and is ready.
I think all women's HCG (pregnancy hormone) blood levels should be monitored after a miscarriage until they hit 0 (not pregnant)
and if women are not offered this, they should use home pregnancy tests to check that their levels have returned to normal before tcc.
Waiting for your period will provide very valuable information for doctors to help them rule out diseases like molar pregnancies, and provides reassurance to the woman that her body is working well.