I'm a beginner guitar player, and I'm trying to pick up some of the music theory behind the instrument, and one thing that I've sort of grasped is odd time signatures.

I know what they are, and I can read and play in them, but I still don't think I understand the purpose. 

For example, let's say you have a riff or something, and it's in 5/4, so this riff is 5 quarter notes. Is there a difference between writing this riff in 5/4 or just writing the first 4 quarter notes of the riff in a measure of 4/4 and writing the final quarter note of the riff in the following measure, still in 4/4?

Is it just for organization/ease of reading's sake?