Not connected to SpaceX in any way, but I can speculate.
1. Drastically less capex for the same traffic volume. If you have enough business to be launching once a week and it takes you on average six months to get a rocket turned around, you need at least 25 rockets (probably closer to 35 to smooth out the peaks). If it takes you on average a day to get a rocket ready, then you only really need two (one and a backup).
2. Beyond being useful on its own, immediate turnaround means that you don't have to do much between launches, which means that you've cut down drastically on opex. It's not just that you can get a rocket ready in a day, it's that you can get a rocket ready with less than a day's worth of work.
3. Agility means that you might be able to take opportunities that might otherwise be unavailable due to short notice. Your probe only has an hour launch window every couple of years, and it's delayed so that it won't be ready until 2 months before? With other launch systems, you might have to cancel due to uncertainty. With SpaceX, no problem - as long as nobody else is scheduled for that day, you can always jump in if your probe is ready.
SpaceX also only has so much warehouse space, and they can't have too many rockets in the shop at the same time. That would limit how often they can do flights.
1. Drastically less capex for the same traffic volume. If you have enough business to be launching once a week and it takes you on average six months to get a rocket turned around, you need at least 25 rockets (probably closer to 35 to smooth out the peaks). If it takes you on average a day to get a rocket ready, then you only really need two (one and a backup).
2. Beyond being useful on its own, immediate turnaround means that you don't have to do much between launches, which means that you've cut down drastically on opex. It's not just that you can get a rocket ready in a day, it's that you can get a rocket ready with less than a day's worth of work.
3. Agility means that you might be able to take opportunities that might otherwise be unavailable due to short notice. Your probe only has an hour launch window every couple of years, and it's delayed so that it won't be ready until 2 months before? With other launch systems, you might have to cancel due to uncertainty. With SpaceX, no problem - as long as nobody else is scheduled for that day, you can always jump in if your probe is ready.