Google Sheets is similar to Microsoft Excel, My Drive is an online storage location, Google Docs is similar to Microsoft Word, and Google Slides is similar to Microsoft Powerpoint
1. To prevent electric shock or electrocution.
2. To avoid component damage.
1. To prevent electric shock or electrocution - A PC that is plugged in means AC power is still available on powerlines inside the computer and a poorly grounded or unshielded power supply can expose the whole computer case to AC and any contact will result in electrocution. This is mainly for the protection of the computer technician.
2. To avoid component damage. - A PC has several components inside that are sensitive to motion while powered or plugged in. This are components are charged up. They can only be discharged internally once unplugged. This mainly focuses on the protection of computer and its peripherals from accidental short circuit and improper static discharge.