Hidden Files Taking Up Space On Ipod?!?

So I've always been aware that there are hidden files on Ipods and that they have something or other to do with the operating system and such. My ipod is a 30gb but it only has around a gb left and I have around 26.5 gbs of music and absolutely no videos or pictures on it. It is a 30gb classic Ipod video. My friend brought up that you have to jailbreak it to access the hidden files but I'm quite familiar with viewing the hidden files by going to the Ipod folder on mycomputer when I plug it in and right clicking the folder, going to properties, and checking the box to make Hidden Files show up. (been a while but it's something like that). I've done this many times in order to import all the F files to my itunes to recover my itunes library after system restores on my computer and such. The trouble is that I have no idea what the other hidden files are and if I could delete any of them without it causing major glitches and malfunctions on my Ipod. Are there any hidden files that it's ok to delete? Please try to back anything up with a link to another site or possibly a youtube video as I'm not gonna just delete something based on word of mouth. For all I know you could pull a "delete sys 32" on me.