A lot.
But I'll just talk about my favourite collection and series, Monogatari:
This one is important not only because it's my favourite anime (and one of my 3 favourite series along with Fringe and Eternal Love (Ten Miles of Peach Blossoms)) but also because all the arcs/episodes aren't available on official streaming platforms, at least not last I checked. Also it took some time and effort to collect because I originally started through a local Australian/NZ retailer called Hanabee, but they went defunct a few years ago before they could finish releasing every arc so I had to finish my collection through Amazon UK/MVM, but because of lockdowns Amazon UK wouldn't ship directly to New Zealand at that time, so I had to also use a proxy service to finally get the whole collection finished.
...Also it's not finished, because Studio Shaft just announced they'll be continuing their adaptions starting with Monster Season, and trust me, there's a lot more to be adapted; Nisioisin and Shaft will never let this series die.
Through Hanabee:
- Bakemonogatari on Blu-ray and a Limited Edition DVD release
- Nisemonogatari on Blu-ray and a Limited Edition DVD release
- Nekomonogatari Black Blu-ray/DVD Combo
- All Monogatari Season Two Blu-ray/DVD Combo-- Nekomonogatari White, Kabukimonogatari, Otorimonogatari, Onimonogatari and Koimonogatari.
- Hanamonogatari Blu-ray/DVD Combo
- Tsukimonogatari Blu-ray/DVD Combo
- Owarimonogatari Volume One and Volume Two Blu-ray/DVD Combo
Through Amazon UK/MVM:
- Kizumonogatari Part One, Part Two and Part Three Blu-ray Limited Editions
- Koiyomimonogatari Blu-ray
- Owarimonogatari Volume Three Blu-ray
- Zoku Owarimonogatari Blu-ray
All of these are in order of the original series/movie release dates, which might be slightly different from when the collections came out. It's also slightly different from the order of the novels; most notably Kizumonogatari was originally published just after Bakemonogatari, and for the official English translation was the first novel released. It's also very different from the chronological order of events, which can make it confusing if you're watching for the first time.