If not, let's say I'm talking about a single backup of a single world. Would that be a reason for you not to increase my disk space having the unlimited plan?
As long as your backup and plugin data doesn't take up an excessive amount of space (ideally < 50%), you'd still be eligible for a disk limit increase. We also provide the initial bump (upon request) to 40GB without any restrictions. Also to note, we recommend using MySQL for data-intensive plugins such as Dynmap and CoreProtect. MySQL usage isn't counted in your disk limit.