Summarize this article in one sentence.
Despite its similar name, a hard reset has very different effects than a soft reset. Hard resets restore your phone to its factory state. This means that all of your personal data, including your apps, messages, and contacts, are deleted and your phone becomes essentially a "blank slate." For these reasons, it's generally a good idea to perform a hard reset only when a major problem makes it necessary.  Situations that might call for a hard reset include: You experience frequent errors that don't seem to get better with other fixes Your phone's software is corrupted Your phone is infested with viruses or malicious applications you can't seem to get rid of There's no "coming back" from a hard reset, so it's vital that you prepare by making a backup copy of any important files, images, or documents on your phone that you want to keep. Once you perform your hard reset, it's unlikely that you'll be able to get them back. In addition, you'll want to make sure your battery is at least most of the way charged — running out of battery in the middle of the hard reset process can lead to serious errors. There are several ways to hard reset your Galaxy Ace. The first is probably the simplest — simply go into your phone's settings menu (the icon looks like a silver gear), then tap the "User and backup" or "Backup and reset" option, then finally tap "Factory data reset." You'll be asked to confirm your choice.  To recap, the menu options you need to choose are: Settings (looks like a metal gear) User and backup/Backup and reset (name may vary based on the version of your phone's software) Factory data reset Confirm your choice Another way to perform a hard reset on your phone is to type this code into your phone exactly as you would if you were dialing a phone number. Hit the "call" button to start the hard reset process. Note that you should not get a confirmation message with this method. One final way to perform a hard reset is to hold these three buttons while the phone is powered off. Release these buttons when the samsung logo appears. This option is convenient if the problem with your phone is preventing it from starting correctly. Note that you will still need battery charge to do this. Leave your phone alone as the reset process begins. It should eventually boot into a special stripped-down menu with various system options listed. Use the phone's volume keys to scroll to the factory reset option, then press the home/power button to confirm. On the next screen, scroll down to “Yes” and confirm your choice. At this point, your phone will begin to work through the reset process without any further input from you. At this point, all you need to do is wait for the operation to complete. This can take several minutes — be patient. When it's done, you may select the "Reboot system now" option from the menu or simply use the power button to restart your phone. After a successful hard reset, your phone should look and behave exactly like it did when you first bought it. It should have only the basic starting apps installed, should use default wallpaper and ringtone options, and so on.

Summary:
Use a hard reset as a last resort for serious issues. Charge your battery and back up your important data. Use the "Factory data reset" option under the settings menu. Alternatively, dial *2767*3855#. Alternatively, hold the home, volume up, and power buttons. Select “Wipe data/factory reset” from the recovery menu. Wait for the reset to finish.