Starting out it is very easy to forget about the sanctum mechanic as you are constantly trying to follow what your opponent is doing and "wait, what was that card?" As you start to get a grasp of everything that is going on, you also start to see ways you can use the sanctum.
It is at this point the sanctum can turn against you!
Grabbing whatever you can afford as soon as you have enough favor might be just what your opponent needs. Without getting too deep into the mind games that take place I will give one recent example.
I had a strong late game creature on board with lethal next turn. Opponent was down to what ever card he would draw on his next turn. I saw that I had enough favor to grab card shark (1 cost frontline) and did it without even thinking about what might show up to replace the card I grabbed.
Sure enough a damage spell pops up, opponent grabs it and does lethal on me.
As I'm left aghast asking myself "OMG, what did I just do?". I start to wonder, did I have any actual need for card shark? Even if I did, was the risk worth the benefit? I traded a known situation for an unknown variable.
At the very least, when we ask ourselves "what do I need from the sanctum?", we HAVE to ask the accompanying question. What does my opponent NEED?
In general, players want to do. They want to use every mana, use favor, get cards on board. Sometimes less is more. Sometimes we need to slow down and maybe just forget the sanctum.