From what I observe from the EPG, I think the purpose of Astro Grandstand 810 is like, it is "to recommend content for you to watch".
As in like, you want to watch sports but don't know which one to watch. Hence, Astro Grandstand channel will be the go-to channel for you.
This seems to make sense especially when Astro has a lot of sports channels, but you don't know which to begin with...
Also, those TV screens you see at commercial establishments like mamak or restaurant showing Astro sports channels, they can just tune and stay on CH810 and wouldn't need to purposely tune to other channel just because there's big matches from different sports events.
Hence, there may be cases where both Astro Grandstand and Astro Premier League channels may simulcasting the same live sports match.
And then at other times, Astro Grandstand and Astro Sports Plus channel may simulcasting the same live sports match.
But I also notice that some live sport match aired only on Astro Grandstand and nowhere else.