You don't need any of those items in your kitchen.

For most people having both a microwave and a speed oven is redundant. In some cases it might be advantageous, like if you plan on microwaving a lot at the same time you're speedcooking or convecting in the speed oven. But for most people, one or the other works fine.

What can you do with a steam oven... Way too much to detail in this one post! Some examples are baking bread with steam for a nice crispy crust, roasting with a low temp or high humidity, or just steaming vegetables. In addition, you can use it as a regular small convection oven without any humidity.

There is a lot of information on the internet about how combi-steam ovens work and the many ways you can use them. They have been discussed a lot here, so I would recommend searching the forum for prior posts on the subject. Also, look up Purcell Murray on Youtube, they have a lot of informative videos about Gaggenau, Thermador, and Bosch steam ovens. Also, the manufacturers put out cookbooks for their steam ovens, you can find some of them by Googling.

As for having both a speed oven and a steam oven... It's a personal decision. Some people have gotten both, but not often. It's far more common for people who want an extra oven to pick one or the other. Having both would be the ultimate setup, but most people just don't have the budget, space, or use for that.

Is there any reason to have both a microwave and a speed oven? What do
people use steam oven's for? There are so many "oven" options... its a
little confusing. thanks!

I have three ovens, a full sized "regular" oven, an Advantium speed oven, and a combi-steam. I do not have a separate microwave.

Is there any reason to have both a microwave and a speed oven?

Yes. Besides the reasons Hvtech gave, there's the price difference between a Costco countertop special and a built-in speed oven. As you use a microwave the magnatron degrades. If you use a microwave to do heavy lifting, daily, you might want to save the speed oven and use a cheapie. You'll know if this applies to you if you've ever had to buy a new microwave. I mostly use my microwave for quickie heating on a sandwich or other grab and go food, and occasionally for a quick defrost. It does get used several times per day, but not for very long. By the time I get to where all ovens are full, I'd better not need a microwave! I don't use it for cooking/steaming, or making hot water, or anything like that, so overlaps aren't a concern. I put the Advantium in in such a way that it's in the position a countertop microwave would sit in, and there's no room for another.

Be sure that you want the speed features. I did when I planned and installed it, but shortly thereafter I really lost the need for speed. There are some things that are best accomplished this way, but the main reason for speed really is to get it out faster.

What do
people use steam oven's for?

There really isn't anything that you can do with a steam oven that you can't achieve another way in the kitchen. People use steam all the time, whether it's wine in the roaster pan, a squirt of water under a dome on the griddle with the burger, a petal steamer full of vegetables in a pot in the microwave, a pan of ice under the bread baking in the main oven, the bamboo box in the water filled wok with all the veggies inside, the colander over the stockpot with the towels and tamales, or the garlic bread wrapped in foil in the warming drawer.

You can do all those things in a steam oven. The one thing that's easier the "real" way is the burger, which only wants a blast of steam at the end.

You can get some Modernist Cuisine aficionado to come explain "wet bulb" vs. "dry bulb" cooking. I don't care. I just cook.

Oh, and the combi-steam is the best for blanching and poaching. Several times a month I have a blanch-fest of asparagus, green beans, squash, etc. I'm allergic to fish, but I do poach chicken for chicken salad. If you don't have an automatic egg steamer, the combi-steam is the perfect way to make hard "boiled" eggs. Maybe soft ones too. Almost every week, I do a roast chicken and veg in it. Today I made custard bound strata in it--layered in a double ramekin, somewhere between a quiche and a casserole. Turkey parts for the holidays. Dim sum. Crusty bread. It goes on and on.

The best trick, found on the Gaggenau and maybe others, is "regenerate". You can do this is a regular oven, too, but not so elegantly. Plate up a meal, put in on regenerate mode, receive perfectly warmed meal with none of the bits gone funny. My big test on it was leftovers from a restaurant: slab of potroast, broccoli and mashed potatoes with potroast gravy. Everything was pleasantly heated through, nothing was overcooked, hard, charred or even additionally browned, etc. I've also used it to reheat casseroles, especially small ones. They don't dry out and get hard.

This is only the very most obvious stuff. There's lots and lots more. You don't need a combi-steam to do it, but it's oh, so convenient!