I’ll wade into this one as well since I have been 10 gallon batch capable for a few years now.
I went from extract kits to partial mash to all in one to multiple kettles - where I’m at now.
I started all in one / BIAB brewing in an Anvil 10.5 gallon kettle. Picked up a spare 110v, 9 gallon kettle on sale for $99 on a Black Friday and rocked this setup until the Anvil 18 gallon went on sale.
I find that the 18 gallon kettle is more powerful and thus faster and easier on the brew day schedule and a touch more efficient than the 10.5 gallon. I began using the 18 gallon and 10.5 together so I mash and boil in the 18, but sparge from the 10.5. The sparging definitely helps the efficiency but costs time. If I took the efficiency hit, I could save ... 1.5-ish hours maybe.
Obviously the equipment is bigger, heavier and longer to clean.
I started indoors and was quickly banished to outdoor brewing. when I moved in 2020, I secured storage for my beer stuff and had an outside circuit wired in. Then, I built a metal out building; Garage, dance hall, brewery, shop and hangout. This gave me 220v flexibility, and more room, so I added a pair of full sized fridges, and increased my tap count to 9.
Now, if I had enough demand, I’d do 10 gallon batches, but as it stands I just don’t have the demand for it, so I do 5 gallon batches; well... I generally target about 6.25 gallons post boil, which lets me transfer about 5.8 gallons to the fermenter with minimal sediment or trub so that when fermentation is completed if everything goes to plan, I have just a touch more than 5 gallons of usable beer, again with minimal sediment.
If the brew does not go to plan, blame
@Josh Hughes
Just remembered the third thing... the beer wasn't better...
This I partially agree with. It’s hard to do an apples to apples comparison since I learn new stuff practically every brew day. I would say that my beer is better, but is it better because I’m configured for 10 gallon batches? No. My beer is better likely because I’ve made plenty of mistakes, corrected them and applied what I learned on previous brew days. My equipment now does make brewing simpler, easier and more efficient in my estimation. That is to say, it works well for me.
My last purchases for brewing have been in the direction of making the brew day better. I got a pressure capable fermenter last year and glad I did. I also got a riptide pump, which is huge, but moves a ton of liquid. I’ve been jonesing to try this out in a NEIPA whirlpool since purchasing but that’s going to have to wait until I have kegs to fill. At the moment I only have room for 1 more 2.5 or 5 gallon keg in the fridges. I do have kegs to clean and I would really like to do something with the German lager yeast I have on hand... but we’ll see.
I also agree with the steam comment, you will still be boiling for an hour + so if you are indoors you’ll need ventilation.