"The cost of the excess space was probably around $1-5, averaged out of the cost of a large disk."So what do you do when that disk dies and you lose all your data?
Oh, you want backups? Well, maybe you could do them yourself.
Oh, you don't want to do the backups yourself but want the sysadmins to do your backups for you, do you?
Or what happens when the network that's hosting the disk becomes inaccessible? You want to get to your data anyway, so that means adding network redundancy.
And you also probably don't want downtime if the server hosting the disk goes down, or the server is up but the disk dies, so that means RAID or maybe a distributed filesystem.
And what about making sure the data is secure and the servers hosting it meet compliance requirements?
And when something goes wrong you want someone in ops to troubleshoot it, right? Maybe you want six 9's of availability, and you want us to wear a pager so we can work on fixing it at any time of the day or night, right?
All of this will take planning and time and more hardware, configuration and monitoring, perhaps a bigger headcount since sysadmin teams are often already running short-staffed and don't have the time to dedicate to supporting even more infrastructure than they already do.
You see, it's not always so simple as "just add another disk".