Up until 2006, Germany regulated all shops' opening hours under a 1956 union-driven law; all shops needed to be closed on Sundays and public holidays, no shops could open after 8pm or before 6am on work days, and if 24th December was a work day, opening hours could be at most 6am-2pm. Then the federal government devolved control of opening hours regulation to the states, and most of them deregulated.
According to a new paper by Mario Bossler and Michael Oberfichtner opening hours deregulations substantially boosted the market for retail workers, comparing states which did deregulate with those that kept the strictures as-is:
We study the effect of deregulating weekday shop opening hours on employment in retailing. Using administrative data on all German food shops, a difference-in-differences analysis shows that relaxing restrictions on opening hours raised employment by 0.4 workers per shop corresponding to an increase by 4%. This effect is driven by part-time employment and employment in large shops, and it implies an increase by 0.1 workers per additional actual weekly opening hour. While the wage bill increased by less than employment, the deregulation seems not to have reduced earnings of workers already employed in retailing before the deregulation
Of course, these weren't specifically Sunday Trading regulations, which stayed intact, but it's not crazy to extrapolate from this that rolling back the size limits that stop bigger shops from opening late in the UK would boost employment here. So that's a sixth reason to hate Sunday Trading Laws.