Android - Micro USB cables that only charge but no data, no mounting etc (Samsung Galaxy S)
Broadly speaking, if you have a "USB" cable that only connects pins 1 & 4 then you will get power and no data (Best Buy was selling cables like that as Universal USB Charging Cables a while back, not sure if they still do). Likewise, if you have a cable with only 2 & 3, you will get data but no power. If you're curious, here's a Wikipedia page with the standard USB Pinout.
Note: Micro uses the same pinout as USB A.
As devnul3 says, a power-only cable is a USB cable where the data pins are not connected. The main reason they exist is because they can be made ever so slightly cheaper by virtue of only needing 2 connections instead of 4 (and also because you don't need to worry about preserving the quality of the very high frequency signals on the data lines).
This said, there are cases where a power-only cable is preferable to a "fully featured" USB cable: when you want to charge your device from some random USB connector somewhere. As is becoming more widely known, a USB connector can be used for many things besides the ones the user expects, so if you use a "normal" USB cable, you may end up unwittingly providing priviledged access to your device.
IOW when you're charging from a USB connector that you have no reason to trust, a power-only cable is not only ever-so-slightly cheaper, but it's also a bit safer.
Sorry to disagree with the other answers, but those assumptions are simply wrong:
- To be compliant with Battery Charging Spec. or any other comparable charging mechanism, the data lines require certain voltages or a shortcut (e.g. BC with <200 Ohms) to identify the charger type, i.e. the charger provides that signals - hence the data lines are required for the attached device to identify the charger.
- Even if only data shall be transmitted, at least data lines and GND are required (see USB 2.0 Spec. Figure 7-19). Hence, is no good reason to keep the VCC line disconnected.
- If the cable-connectors have the USB logo on them those cables HAVE to be compliant with USB standard, which in turn means that all pins have to be connected.