Keeping Media on external storage?

I have heard or read multiple times that keeping media such as all my songs on an external flashdrive or harddrive of some sort will keep my macbook pro from bogging down. My macbook is not by any means slow I just wanted to prevent anything in the future. What are the details of this claim and is it effective?

sj, it really depends on how much music you have.

typically people like to keep what I believe is 20% of their HD (so a 250gb HD, would be 50gb of free space) free to keep the computer from slowing down.

You can have as much music/music/etc on there as you want, as long as you keep a nice little "buffer zone"

The only way having a lot of media on your main HDD can slow it down is if you don't have enough space left on it for OS and apps to operate, or if it becomes extremely fragmented.
Since fragmentation is not an issue on Macs, as long as you keep a small buffer just like whitehorse84 said, you will be fine even without an external HDD. Do get one of course if you are running low on space.

Mind you having the external partitoned into 2 parts. One for easy access to media and the other for time machine (exactly how my external is partitioned) is a good idea though.

I have very little music on my macbook itself. I have a large library and most of my music exists on my buffalo linkstation. It is a network hard drive. I have a few different machines and this way the can all access the same music. I also have a 2.5 external 500 gig drive with the mostly same stuff that is on the nas but its portable for traveling.