For me, the debates are not about knowing the policies, they've not changed for years, blue for small state, unregulated capitalism and red for larger state, socialism; with a few swingers in the middle to try and tempt the oppo voters. Also the manifestos will be available in PDF for our viewing pleasure anyway.
In the last GE debates I liked seeing how they reacted to small bits of off piste discussion, having their anger piqued, occasionally getting the briefest glimpse of what they're like when things wander away from the scripted responses and they have to be borderline honest. Clegg did come over fairly well and got a bounce, which was good, he seemed like the closest one to a rough approximation of a human.
May seems quite a capable speaker, so I'm not really sure why she's wet her knickers on this, other than she struggles when not reciting the gibberish like "Brexit means Brexit" and "God told me chocolate eggs are Christian".