I do it because I don’t want to run short of IP space.
I’ve worked on networks that are reaching the limit of how many systems they can hold, and I don’t want that to happen, so I intentionally oversize basically every subnet and usually over segregate the traffic. I use a lot of subnets.
They’re not all VLANs, some are on independent switches. What I did for storage in one case is gave a single NIC to the management Network for administration, and the rest connected to a storage subnet with fully dedicated links. I was using the same switch so they were vlanned but it easily could have been done on another switch. The connections from the storage to the compute systems was all done with dedicated links on dedicated NICs, so 100% of the bandwidth was available for the storage connections.
I’m very sensitive to bottlenecks in my layer 2 networks and I don’t want to share bandwidth between a production interface and a storage interface. NICs are cheap. My patience is not.