WOW...this has turned out to be a great discussion!!!! It is apparent from the answers that everyone understood my question.
The reason I originally ask the question is to try and understand why I have three formats and do I need three formats?
Personal observation, I have several photographic hobbies.
Snapshots/pocket stuff, using it for note taking with other projects, parties and so on,,, usually use the "DarkSide" products that shall not be mentioned. More of a nobrainer user mode,,, not so much photography as a pen and paper.
Pack a camera around in the back seat so it's there with me, tripod getting beat up as well. 35mm Nikons and two or three lenses. One body with slow color, the other with faster film of some (random) kind.
Then there's the mental photography game. 4x5, tripod, spot meter, sometimes the 35 gets dragged kicking and screaming into this realm. It's a mental break from reality for me in this mood/mode. Being focused on a project and blocking out everything that happened last week, at least for a short while.
Now we get to the fun stuff. My baby speed graphic with roll back, hand holding the linholf, Delta 3200 in 120, my old graflex22. Working on my Argus C3 and others, a minolta 16 or three. Dark room, doing some developing, building a light meter, repairing a densitometer, and so on and so forth. Next project is a refinishing project on a B&J 5x7 commercial.
So, for me the format is like a lot of the rest of the hobby. It just is. Not good, not bad. Some days I want to work on the electronics of a densitometer, some days I want tri x in a 16 mm,,, some days I wish I had my buddies C33 back.
So, and the final answer for me,,, YMMV: Of course you need at least three formats. I'm just not sure how you get by with only three ;-)