I see that 8arrows and I were posting at the same time!
This is a great question, and one that has many answers. First off, I think it's important to realize that with HOD you don't have to run 3 programs to get a good education for your children. Just as you have choices with other curriculums, you have choices with how many programs you are comfortable running with HOD.

There are many ways to combine within a program if desired, and it's so important to be aware of your own teaching style and lifestyle when deciding how many HOD programs to do.
So, if combining your children is a priority for your family, or if you have an especially hectic shedule and need a more streamlined school schedule, or if you are facing an unusual amount of medical concerns, or if managing several guides makes you very stressed, then choosing 3 HOD guides is likely not your best fit. The important thing to realize is that you can still choose HOD, but you just choose the options to combine instead. Next, I think it is easier to run three HOD programs (if you choose to do so) once you've already done one or more HOD programs first. In that way, just as in life itself, familiarity makes doing something similar much more manageable.
We would not recommend jumping in to do 3 programs if it is your first experience with HOD. We would instead lean toward having new HOD moms or new homeschool moms do a single program or possibly two at the most, and then decide if they desire to branch out into 3 programs later in the year or another year. We would typically instead suggest combining kiddos (as best as possible) for the left side of the plans, and then adding on a corresponding piece of language arts and math from a higher HOD guide. This works no differently than other programs who combine for history and have separate language arts and math for their kiddos.

We may also recommend doing two programs, depending on your situation and your family goals.
So, it still remains a choice as to how you wish to use HOD. It will also make a big difference which HOD programs you are looking at utilizing. For example, we would not usually recommend doing 3 programs at the same time that are in a row together. For example, we wouldn't usually suggest doing LHTH, LHFHG, and Beyond all at once, because if your kiddos are close enough in age to do 3 guides that are in a row, then some of them should be able to be combined into 2 programs.

The same is true as you move into upper guides. For example, we wouldn't recommend doing Beyond, Bigger and Preparing at the same time, since kiddos who are close enough in age to do those programs, should be able to be combined within one or two programs.
We have families that combine and those who do not. HOD works well in a myriad of situations. We have run 3 programs at our house for years and this year we'll be running 4 programs. From having used many other curriculums out there, I can tell you that there is no way I could personally do that with just about any other program available (and still keep my sanity).
So, would I typically recommend that other moms jump in then and do 3 or 4 programs to start out? No, but I share this to let you know that it is possible and reasonable to do multiple programs once you get used to the flow of HOD and are no longer new to the guides.
Easing into adding programs through the years is very reasonable. Once you've been through a guide, when you pick it up for your next child in line it feels like visiting an old friend. You know exactly what to expect and can just enjoy the time spent together.

Then, adding a new program along with it is not a big deal. This is the situation that we are in right now. We've already done LHTH and Beyond in the past, so adding CTC and piloting our new guide along with doing those programs (for us) seems natural. For me it is an added relief to know exactly what my little ones will be doing without all the prep. and planning on my part.
One thing that sets HOD apart from other curriculums is that we do not do a one-size-fits-all placement. So, the goal is to find out what works best for you!
Blessings,
Carrie