Just applied online for my Unifi VIP10 connection . Hopefully everything goes smoothly

One Newbie Question , i see a lot of Suggestion to Flash their Routers to OpenWRT, what is the actual benefit in doing so?

I read a few locations whereby there are people claiming that their connection speed gets better, their more stable. But can any Guru's here explain is this really true and what is the logic behind it? (sorry if this became a hijack thread, but as i've just applied for my VIP10 line , i'm preparing all the neccesary to get the maximum benefit )