Every time you turn on your computer, you must choose a user account and log in. This is true for Windows, macOS, Linux and even Chrome OS. This is why it is necessary for PCs, but not for iPhones, iPads and Android.
They are designed for multiple users
Modern operating systems have been designed for multiple users. Even if you never connect to your Windows laptop with a single user account, Windows is designed for more than that. This means that the same operating system works for the computer of only one person, a shared family PC or a desktop workstation.
Different user accounts are used constantly in the background. Most of the applications you use work with the security settings of your user account. Some work as an administrator, giving them full access to your system, and you must agree to provide User Account Control (UAC) authorization on Windows before launching them. Different background services and automated tasks work under different "user" accounts with different security settings.
Your password can also be used for security in the background. For example, FileVault encryption is enabled by default on macOS. With this setting, your Mac files are encrypted until you enter the password for your user account. Without the password, you can not "unlock" the drive and view the files. However, FileVault does not use a different password. It just uses the usual password of your Mac.
iOS and Android also have user accounts
The iOS operating system of Apple and Google Android are different. They are not designed to be used by more than one person. First, they were designed to work on the phone or tablet of one person. But under the hood, Apple's iOS operating system and Google's Android also use user accounts.
The process of starting and unlocking an iPhone, an iPad or an Android device is similar to connecting to a modern PC. You start it and need to enter an authentication code before the device will unlock and become usable. The only difference is that it is usually impossible to select multiple user accounts when starting the device.
These user accounts are sometimes visible. For example, iPads have a multi-user mode which can only be used by schools. Android offers multi-user support on phones and tablets, although manufacturers like Samsung often remove this feature from their devices.
Even if you do not have access to these multiple users, the basic operating system uses them for different tasks. Google Android is based on Linuxand Apple's iOS is also a Unix-like BSD-based system. Both are multi-user operating systems.
You can ignore the connection, but you should not
It's possible to connect to your computer automatically, but that's not the best idea. For example, you can automatically connect to your Windows PC, but this stores your password on your computer in any way that any of your current programs can access it. Macs also allow you to enable automatic logon, but this requires the deactivation of FileVault encryption because the password is required for this.
And of course, if someone has access to your computer, he can turn it on and immediately start using it. It's not good especially if the computer is a laptop.
Make the connection faster and easier
Even if you are the only person using your PC, modern operating systems simplify the ignorance of other user accounts. Your computer will automatically select the last user account you have used and you will only need to enter your password.
This can be a bit awkward if your password is long and powerful to protect your Microsoft account, Apple ID or Google Account. Modern computers allow you to simplify things.
We recommend to set a PIN code on Windows 10 or activate Windows Hello for a faster connection process. Modern Macs have TouchID fingerprint readers and maybe unlocked with an Apple Watch for a faster connection process. You can set a PIN to sign in to your Chromebook or use Smart Lock to unlock it automatically with your Android phone, too.
Once configured, you can log in to your computer as easily and quickly as unlocking your phone.