What Is EFI System Partition? Can You Delete It?
To cut a long story short – YES, you CAN delete and EFI system partition, if you really put some effort into it. NO, you really should not do it.
For the most part, deleting a partition in Disk Management is a rather straightforward task. You just select the volume in question in Disk Management, and click "Delete Volume" – however, for EFI System Partition in Windows 10/8.1/8/7/XP/Vista, that feature is usually grayed out, if it is even visible. And there's a good reason for that.
What is an EFI System Partition?
An EFI System Partition is a small, FAT 32 formatted partition on a data storage device that is used in computers adhering to Unified Extensible Firmware Interface. It is automatically generated when you install your OS, be it a Windows or a Mac OS. When you boot your PC, UEFI firmware loads essential files stored on the ESP to start the installed operating system and various utilities necessary for the startup of your machine. The EFI System Partition contains Boot loaders, Device drivers, System utilities, and some key Data files that are absolutely necessary for booting Windows.
This basically means that deleting EFI System Partition will render an installed OS unbootable. This is the reason why EFI System Partition is usually protected in some manner – in many cases it is not accessible or visible if you don't specifically look for it, or is locked by the Windows operating systems to prevent accidental deletion.
So, as we have established, EFI System Partition is essential for the functioning of your OS. Under normal circumstances, a user should have no reason to delete it or interact with it in any way, shape, or form. It is a very small partition containing no more than 100-200mb of data, so deleting it will not free any substantial amount of disk space. If you find yourself short on disk space, there are other steps you can take to free up some that will not render your OS damaged beyond all repair.
Additionally, this partition automatically is deleted when you uninstall your OS, so it's not something that you need to concern yourself with anyway.
Should You Delete EFI System Partition?
So, to recap once again – EFI System Partition is an essential part of your OS. Technically, you can delete it, but in practice, there really aren't any circumstances in which that'd be necessary, or even remotely advisable.
You have completely ignored the possibility that there are multiple disk drives in a computer.
If the computer's firmware is UEFI-compliant and does not support BIOS, either natively or via CSM, then it is necessary to have a ESP partition in order for the computer to boot. The safest thing to do is to ensure that the computer has ONLY 1 ESP, because some firmware gets confused in the presence of multiple ESPs. This implies that for GPT-layout discs which are used only for data storage, the best approach is to delete any ESP which gets created on that disc.