I plan my schedule in advance, and besides shooting days, I also need days for photo editing and days off (you probably wouldn't want a photoshoot with a completely exhausted and burnt-out photographer). So, I don't plan working more than I can physically handle.
I only have one photoshoot a day. Almost everyone wants to schedule shoots on weekends, so those slots fill up first (often weekends are booked two months in advance). It's a bit easier to book on weekdays, we can usually find a slot within 3-4 weeks. The busiest times for me are before and after vacations, so I always let clients know about those months in advance.
Occasionally, I have to reschedule shoots, so in any case, you can always reach out to me to check for available dates.
I book shoots with a €60 deposit, so I can be sure the person is committed. Many conversations with potential clients end in silence. I'm always surprised when someone disappears for weeks after finding out my availability, and then assumes I've been holding dates open for them. That's not how it works, as I immediately book a studio for the required date and time if we agree on everything.
What can happen if you book late? I simply might not be able to find an available slot at the time you want. And if waiting a few weeks for an individual shoot is not a problem, for a maternity shoot, it might be too late, and I don't have other choice except recommending to find a photographer with a less busy schedule.