For security? If you're not using a password manager, that means you're using the same password for almost every site. Which means every site is a point of failure for every other. This means some way of generating and saving random passwords for each site (i.e. a password manager) is absolutely required for security. You are welcome to use the password manager that comes bundled with the device you paid for (apple, android), or use paid cross-platform ones like 1password (which works well), or use free cross-platform ones (in which case you might get what you paid for).