About

While Android 4.0 (aka Ice Cream Sandwhich) introduced the feature to "disable" some system apps and bloatware (which can be done from Settings › Apps › Manage Apps by selecting the corresponding app and hit the "Disable" button, when that one is not grayed out), this does not work for all apps – and is not available prior to Android 4.x.

But long before ICS was even announced, apps like e.g. Titanium Backup allowed the user of a rooted device to do the very same, but for all system/bloatware apps. It then was (and still is) called "freezing an app". Of course, if the user wishes he can "un-freeze" a frozen app at any time.

Please do not confuse this with a "hanging app" which no longer responds to user input – which is a completely different issue called "ANR" (Application Not Responding).

What is this good for?

• disabled apps do not automatically start (e.g. when you boot the device), and are no longer registered to broadcasts (i.e. they no longer react on stuff like "network status changed", "sd card mounted", etc.) – which saves battery and other resources.
• disabled apps are no longer shown in the app drawer or on your home screen – so less clutter

What's it not good for?

• disabled apps are still installed on your device, so this won't gain you any space (apart from that: even if uninstalled, you would not be able to use the "freed space" as the apps are installed in the /system partition, not in "user space". However: If the "disabled app" has received updates, you now can delete those updates; as updates are stored in user-space, this will gain you some storage.

Can I disable all pre-installed apps? Is there some danger to it?

First, not all apps can be disabled – for some you will find the "disable" button unavailable or grayed out. It would e.g. make no sense at all to disable "Android System": nothing would work anymore on your device.

If the app-in-question offers an activated "disable" button and press it, you might have noticed a warning popping up: If you disable a built-in app, other apps may misbehave. Your data will also be deleted. That warning is not always true – but yes, sometimes there are dependencies. If you're absolutely sure you don't need the given app, you can try anyway: You cannot disable any app which is really essential. So in the worst case, you re-enable the app and reboot – all that might be lost would be the app's data then.

Related tags:

• bloatware: Apps which manufacturers think to "make users happy", but hardly anyone really wants to use. Still, they come pre-installed on our devices, and (with few exceptions) cannot be un-installed without rooting the device in question. Luckily, they can be disabled with Android 4+ – or instead of uninstalling them, they can be frozen.
  You can use this tag in conjunction with freeze-app if your issue is about freezing bloatware apps.

Unrelated, but similar sounding

• system-freeze: when the entire system stops responding to user input.