Waste of space due to fragmentation is the first thing that comes to mind. I got tired of moving and symlinking stuff to make room inside partitions. Nowadays I only use the essentials (/ and /efi) + /home + 1 partition per physical device, with a filesystem that makes sense for the usage and device. That said, I never run more than one distro on bare metal.

Theoretically you could put all the Linux installations on a single big btrfs partition under different subvolumes.

partitions are used for organizing, the downside is that more partitions make each one smaller

I end up running 1 btrfs partition sagred between all my installed Linux distros on one system

lvm is also awesome for resizing and moving partitions

my desktop right now has nvme0n1p1 as my efi partition and p2 as a lvm pv

inside that lvm I put everything else as it’s very easy to resize and move them (I also have p2 encrypted with luks2)

Not really - sounds like you do need actual partitions since you’re running different OSs. Typically you would use some other form of volume management (LVM, btrfs, zfs) for partitioning within a single OS. But for separate installs it’s fine. gparted does a good job of letting you move things around and resize as needed. Just take care when shrinking partitions to shrink the filesystem first.

There used to be a time where there were obnoxious limits about the number and types of partitions you could have on disk (2 “physical partitions” and some number of “logical partitions” - I forget the details now). But if it works it works.

Lvm could be the way to go. Start with the minimum amount of partitions (i.e. / and /boot and swap as lv, maybe efi as a real partition). Add additional lv later if/ when you need them. You can always re-size a partition and the wrapping lv when you want to re- distribute storage-space.

I never needed more than these partitions. But that is just my use case.

Edit: oh. Missed the Multi boot point. Forget what I wrote. :)