One main disadvantage of USB flash drives or thumb drives is a security issue that can be exploited, namely a weakness with encryption. Their small size can be another disadvantage depending on one's preference, though some consider their size an advantage. They can also become corrupted or lose data.
However, USB desk top back up drives come in large sizes (gigabytes and terabytes) and make for quick and easy data storage.
Besides flash drives being lost, all USB can be damaged if the home has a fire.
A USB soundcard may tax your processor and can introduce some latency.
disadvantages
The advantages of a USB SD are that you can store information. The disadvantages of USB SD card reader is that it can be lost easy.
Yes, you can charge some Canon cameras using a USB cable.
there really isn't one besides you might loose it easily.
it will save some space from your hard drive
You can charge your Touch by connecting it to any computer's USB port, by using a plug-in USB power supply, or by using some form of USB battery pack. I don't know if any of these fit your definition of "without using a charger".
An advantage of using a wireless USB is the ability to sync to a multiple media devices. The disadvantages to using a wireless USB is the device may run slower than normal, there is a risk of damage because of the USB is sticking out of the computer, and there is a greater risk of having information hacked.
USB chargers are not universal for all phones. Some phones will not charge using a USB cord and some will. It depends on the brand of phone. Some Motorola phones need a specific charger or they will not charge.
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There are a few disadvantages of using biomass energy. Some of the disadvantages include the cost, use of fossil fuels, and environmental hazards.
you can hook it to your PC or mac using i-tunes, but it depends on which USB cord you use because some of the, are used only to charge the phone.