Just like with regular programming, or pretty much any kind of knowledge there is no real limit to what you can do with information security knowledge.
You should ask yourself what you want to get out of it yourself. Do you want to improve your skills for better job prospects? Want to become a successful criminal? Do you want to protect yourself? Do you want world domination? Or do you simply want to know because these things are a challenge and worth knowing?
For me(and probably most hackers) I think those last 3 apply. I value my privacy and the integrity of my data, I like the challenge of seeing how things work and how they can be improved or broken.
What you actually do tends to become irrelevant, whatever you do will increase your knowledge and improve your skills.
But consider that your degree is the absolute minimum to get a job(actually, you don't even need the degree for that if you already had those skills) and you can spend your entire career only learning whatever other minimum thing your boss requests.
But if you are passionate about this sort of stuff, wanting to know everything you possibly can know about a subject is pretty normal and you won't need a reason or goal for that.(although a good boss will reward such mentality with better pay etc)
For me the time spent on all this is well worth it. The sleepless nights, the loss of social contacts, the unhealthy habits, the huge power bill, the realisation that most people are pretty unaware of the simplest things and the thousands and thousands of hours of my life spend looking at a screen all to better understand things ever so slightly.. all worth it indeed.
But for some people this might not be the case and I can respect that too.
I like to compare hacking with the rabbit hole in Alice in wonderland(or the matrix, or whatever pop culture icon you prefer that references the rabbit hole). You can stay in the normal world and be no worse off for it. Or you can go down the rabbit hole and see where it leads. (protip; There is no end to the rabbit hole. You just keep going deeper and deeper and the further you go the harder it is to go back. Until the entry point is just a distant memory, wondering what it is you're doing out here in wonderland. But unlike Alice, you have no desire to go back.)
If you still want to learn and are still stuck on the what, thats what the challenges (and many others like them) are for. We'll tell you what you're supposed to do, then you go and acquire the knowledge to do them.
<Yoda> if someone says something i don't like, i ban him, ban whoever defends him, and then ban the witnesses...