In your case (if I'm guessing correctly), it's probably better to keep using the provided Music and Video apps. This is because (if I'm guessing correctly), you get your music from something resembling the iTunes store or a subscription.
If that's not the case, read on.
My case, and that of others I know, is where one has music that was purchased in the heydays of vinyl and later CD's, long before the "iTunes Store" was even a glimmer in Jobs' beady eye. And that music has been converted to digtital if necessary and is stored as files on HDD's or external media. How do you play these files on the iPhone/iPad? Can you do it with the Music app?
Moreover, how do you play video files that you have had since before iOS existed, or that you acquire outside of the iTunes store?
The solutions I refer to are not "hidden knowledge" as you suggest. But they assume familiarity with basic networking and networking protocols.
First, you will need to connect another computer not running iOS to your local network (e.g., plug it into you home router). Being HN, it is assumed you know how to configure and run "servers" (programs that serve files to a network) and that you use an OS that lets you do so, easily. Several such OS's are freely available.
Then, if you simply "serve" the audio and video files from the non-iOS HDD or external media drive to the iOS device via your local network, you can use a free app from the "App Store" (or you can just use Safari) that can behave as a client on the iOS device. Using the right apps, you can either 1. download files to the iPhone/iPad then play them, or 2. play them directly from the non-iOS HDD/media drive ("streaming"?).
I have used HTTP, FTP, SFTP, WebDav clients successfully. But there are probably others that could work.
Some apps also give you server capabilities, so you can download files from the iPhone/iPad to your non-iOS computers.
Any serious work with audio or video (e.g. transcoding) can be done on the non-iOS computer _before_ serving it to the iOS devices. For example, do conversion to MP4 (the format Safari likes) on the non-iOS computer.
Here's a few apps you might use (assuming you understand the protocols above):
AirDrive
Documents
OPlayerLite
If you have some specific issues you cannot solve, I'd be happy to try to help you. But you'll need to give details of what you're trying to do. If you just say "VLC on iOS is a PITA", then I'm afraid there's not much I can do except to say "I agree." Whereas if you say, "How do I ________?", then maybe I can suggest a possible solution.
Regarding these apps, you asked "What benefit do I get from them?"
It depends.
If you "rent" your audio and video from Apple, then they offer little to no benefit.
But if you _own_ audio and video files, e.g., from the pre-iOS era, and you want to play them on iOS devices, then the answer is "They let you transfer and play files." Quite useful, indeed.