You definitely could do that. If I am pushing 23 saga's I would go for max renown. That's just me though. I have my capped saga runner. That is pretty gimpy. But can run the LE stuff solo. I will spend points to maximize return. I have a my toon I tr that will get all saga's complete by 32. I will also have enough points from favor to buy a pot. Why move a level when you can do 5?
A single sovereign guild elixir costs 1,195 points and gives you 400% renown. The turn-in House Cannith potions give you 225%.
You get a little less than double the renown, but from a time perspective it takes significantly longer to earn 4800 favor to buy one potion vs buying a potion with challenge mats.
At least for me that is 1,195 reasons why I prefer the free potions and still have every ship buff. However, everyone has a different way of looking at things and throwing money at the game will always speed up your progress.
I shared this because most people I talk to don't know how to get free renown potions that more than doubles their saga renown. Hopefully someone that doesn't want to spend 1,195 points on a potion will get some benefit from the information.