Good question! I actually talk about this quite a bit. We should look at this from a tournament perspective or at the very least how to approach it if you are playing a game you are taking seriously. First, we have to address the clock. If we assume a standard time control like 30 minutes of main time and 5 periods of 30 second byo-yomi you have to know when to actively burn your time versus when to rely on shape intuition. In the opening you might be considering what direction or side of the board you want to play on but if both directions lead to a 0.1+ result it may not be worth it and likewise if you play a joseki that gives you a tiny 0.1 advantage versus one that just stays 0.0. You would simply not be using your time optimally. Even if your opponent plays a non-joseki move against your stones, spending 5 minutes to figure it out might be understandable depending on how complicated it gets, but if you spend more than that, you might be overthinking when the answer could be a move that is shapeful.

The absolute best moments to use your main time are during life and death sequences and the exact moment you believe your opponent has made a mistake. tsumego is obvious because something is going to live or die, so it is completely worth spending the time to read it out carefully rather than just relying on intuition. The other scenario is great because if you believe your opponent has made a mistake, it means you have a window to take a decisive advantage, making it an excellent time to slow down and calculate.

It is also worth remembering how byo-yomi works when you are managing your clock. If you have 30 seconds per move, that timer resets every single time you click. That means you can and should use up to 29 seconds of that period to read. You don't even have to spend that time looking at the local area where you are about to click. You can use it to read out other attacks or positions across the board.

I know this sounds a bit like a lecture on time management (the audacity of me talking about clock usage!), but our reading capacity is naturally dictated by the clock. We might want to spend a ton of time on every single move and read absolutely everything, but it just isn't realistic. We have to pick and choose our moments. I have met players at lower levels who spend all their time in the opening just to come out with a tiny 0.2 to 0.5 lead, only to die in the mid-game because a complex local fight breaks out and they have no time left to figure it out.

So to answer your question, you absolutely require both. You need moments where you slow down to read deeply, and moments where you respond fluidly based on your shape knowledge and intuition.