Good question. I guess it matters in that people know what is expected of them.
I am a bit bemused about who walks behind whom, where the royals sit, and whom they sit next to. The hierarchy looks a bit weird to me in this day and age.
I think email invites are quite acceptable now. Mail invites, as nice as they are, are out of date. But perhaps the mailed invites have some security thing - a chip or an engraving that emails can’t achieve?
My grandparents were invited to our government house to meet Charles and Diana. (Their first tour will William). They kept the invite, we found it when packing up their house after their deaths. Nan was a voluble Protestant royalist, Pop was an Irish Catholic and kept his mouth shut. Nan had a photograph of the day - of her and pop and Charles and Diana.
Diana was v young and very tall and Nan is pictured cutseying - Nan was less that 5 foot tall and looked like the queen - modelled herself on the queen (clothing, shoes, bag -not the hair though). And she also smoked like a train like Margaret and liked a drink, popped a few pills. She looked like the Quuen but had the temperament of a Margaret lol.
anyway, when Nan curtsied she did a deep sweeping curtesy so she’s all bent over and looks about 2 foot high, and Diana and Charles are looking like they are very trying not to laugh. Diana was wearing a lace collar. Before she learned to dress better.