There are some disadvantages if enabled Autorun feature of Windows, namely:
1. If the CD / HDD External / stick contains a virus then the virus can easily attack your computer via the autorun feature windows 7
2. Windows 7 will allocate memory for the autoplay feature, so it could drain of computer memory.
Actually you can disable autorun / autoplay windows 7. Here is how to turn off / disable autoplay windows 7
1. On the Start menu, select Control panel
2. Select hardware and sound
3. select Autoplay
4. Remove / uncheck the "Use Autoplay for all media devices"
Click the Save button
Good luck
