Ok, so I'm good with how to store them...sort of.

I store them on an external hard drive and DVDs, but ATM they are also all still on the hard drive of my laptop.
I take lots of photos. I'm trying to improve so practise a lot. I have a DSLR and the photos are huge and it's seriously slowing my laptop down.

So my question is, once you've backed your photos up/stored them, do you delete them (all or some) off the computer?
Should I do that? Shouldn't I do that?
I have a PC too, should I be backing them up there as well (don't use it much at all any more)?