Decks are like works of art - hey, they *are* works of art.
Some people can buy one framed canvas for their living room wall, and be perfectly happy. Otherts are happy with blank walls until they get that first one, then buy anotyher for another for another room, than a third one, and voila, they're collecting. I watched "The collectors" tonight, first time in ages I've had time for TV, and Andy Muirhead said that three of anything is where you tip over into collecting: you get one, then you get a second one to go with the first, but there's absolutely no need to get that third, so when you've got the third, you're a collector.
Tarot decks are like clothes, or books, or trees. You can get by with just one in your home. But more than one equals a greater diversity of experience and a greater degree of pleasure.
I fell into collecting - I honestly didn't realise I was doing it.
I learnt on the Rider-Waite. I grew out of it - it stopped fitting. So I bought a couple of others, looking for one that I liked better. Then over a period of several years, I accumulated 24 or 25, and used three or four of them. Then an already-dodgy relationship I was in tipped over into the abusive end of the dial, and I wrapped them all up, stuck them in a box, and hid the box under a collection of dusty detritus at the back of a wardrobe. A couple of years later the police finally got rid of the person and I pulled the box out - to find that they'd reduced in number all the way down to eleven! I was heartbroken. That was a year or two ago: since then I've been buying absolutely as much as my budget will allow and when my budget allows, not to try and return to that state (I've far overtaken it), but to try and compensate the pain of the loss, which still lives with me, thought less and less now.
I am very broke now, and doing no buying, and I haven't replaced all of the ones I lost - I've picked up a large number I didn't even know about back then. There are several still missing that I used to have but really only one I need to replace, the Servants of hte Light Tarot. Unfortunately it's OOP and pricey - it can wait.
I have a feeling that if I get a copy of that, I'll probably ease right back on collecting - it used to be a real character of a deck.
There are a number of benefits in having many decks.
1) You can pick a few decks at your whim to read for other people with, and give them their choice from that selection, and when they come back for another reading later, there will be others on the table.
2) Different decks do different things, and have different strengths and weaknesses. Sometimes I'll choose a definite deck for a particular task.
3) When you look at the same images in the one deck over and over again, you can sometimes reach saturation-point, where you know them too well, where the meaning is stripped out of them. I remember reading an Agatha Christie book years ago, and on one particular page she had used the word "long" over and over again. After reading it several times, it started being weird, meaningless, just occupying paper. I haven't personally had that happen with the images from a deck, but a friend of mine has with one of her two decks, at which point she switched over to using the other one as her main deck - the images just became meaningless to her. With a collection, when that starts to happen, you can just pick up a different deck.