Advantages
Carry zillions of songs in a single tiny device
These days high volume mp3 players with capacities as much as 80GB with the Apple iPods are easily available. Even with a 8GB iPod Nano you can fit in your entire music collection. So if you are on a trip with your family, you don’t have to carry hundreds of CDs to cater to each one’s needs.
No more dealing with scratched CD’s
While driving, it is not possible to take extreme measures in protecting CDs, and as such music CDs in cars invariably get scratched. This leads to skipping of tracks. With an mp3 player, you will not be subject to the trauma of bad music, since tracks in the mp3 player are digitally stored. A track played in the mp3 player for the 100th time will play just as good as it did the first time.
Ease of Song navigation
An iPod Video screen displays seven lines of text as compared to two for this head-unit
Even though navigating through sound tracks in the car stereo has improved over the years, it's much easier and better in mp3 players. High capacity mp3 players have a huge screen displaying at least 10 lines of text as compared to what is available in a car stereo. Besides many enhanced features such as sorting of songs by artists, genres etc. and a search option for finding songs—found on most creative hard drive based players and also in the updated fifth generation iPod—can be found in an mp3 player.
Disadvantages
Discharged mp3 player
Your mp3 player needs juice to run on, provided by the battery. So if you are out of charge, you are out of music! But, there are workarounds for that too. You can use a car charger powered by the car cigarette lighter slot. Besides mp3 players have really evolved, giving anything between 10 hours to as much as 35 to 40 hours (iAudio X5L) enough to last you even a long trip.
Inconvenient to use while driving
The car head unit is designed to let your control with minimum attention on it, so that you concentrate on driving. With the mp3 player it becomes difficult since you have to look straight into it. It would be much better if someone in the co-passenger seat is controlling it for you, else if you drive alone and still want to use your mp3 player, better make a play list before you start.
Now that you know its advantages and disadvantages and still want to use your mp3 player then read on to know how to go about it.
Sir, 
