Why did riot make the upper semifinals for NA the same day as the first round
It has several benefits over the older format for competitors.
All teams on day 1 who would be having multiple matches will all be coming from wins & have a similar level of winning momentum/mentality. The previous format had teams who had just lost immediately fight again for their life after dropping down to the lower brackets and risk getting eliminated.
Additionally, the teams who do end up losing that day get to rest until the next day without being eliminated, so if they were just having a bad day, there's a chance for them to make up for it or reset their mentality so they can play close to their best (which is what we want to see).
Lastly, it lets teams who win and remain in the upper bracket skip the next tournament day to rest while the lower bracket teams work themselves out. It essentially rewards them for staying on top.
For the viewers, we get to know who 2 of the top 3 are on day 1.