All apps automatically sign into your Microsoft Account, and will not prompt for your credentials.
You are forced to login with your email password, which, unlike your easy (or non-existent) Windows login password should be a long and complicated password because it can be hacked at 24/7 from the Internet. However, this password makes unlocking your computer needlessly complicated. The other option is a PIN, which is much less secure than even a weak password.
Because your password changes and the Microsoft Account involves signing into Microsoft servers, your computer may become unusable if your Internet connection goes down or you're in a place that doesn't have WiFi. As a computer technician, this is a huge nuisance for me (they give me password, machine can't connect, password doesn't work).
Anybody who your share your Windows login password with (coworkers, computer technicians, friends, family members) now know your email password and can hijack your Microsoft Account because the passwords are the same. People are shocked when I bring this information to their attention.
A lot more of your personal information and computer usage habits are sent to Microsoft on a regular basis, and they are tied to your Microsoft Account, which has your name, emails and any other activity you do that involves Microsoft.
Your full name and email address are known by Windows, readily accessible to any program running on your PC (including viruses, which will gladly add it to spam lists), and trumpeted on your computer's login and lock screen, not exactly desirable if you don't want all your coworkers to know your personal email address.
Some settings will sync between all your devices, which may be undesirable. For example if you want taskbar autohiding enabled on your tablet but not on your desktop.
Is confusing for administrators setting security permissions, because all the account names change to email addresses, but internally still work as account names.
Is more private.
Always works, regardless of Internet connectivity.
Can have any name/screen name you wish, instead of sharing your email address to everyone who walks by your locked computer.
Can have any password you wish, and it is totally separate from your (hopefully) secure email password.
Can't use some apps.
Apps that do work require manual sign-in one by one.
The app sign-in dialog tries to trick you into converting your Standard Account into a Microsoft Account.
Bottom line: If you're not planning on using the Windows Store or any of the apps, avoid a Microsoft Account at all costs. Most of the apps are junk anyway.
If you wish to use no logon password and have your computer boot directly to the desktop, click Start, type "netplwiz", press [Enter], and untick Users must enter a user name and password to use this computer.