I don't know why authors would leave out punctuation. It's a very big thing. It's probably the 2nd most important thing in your story. 

.     ,     ?     "     '     !

What not to do:

1. You shouldn't write without punctuation. Without it, it makes the whole story confusing and hard to read.

2. Don't write without paragraphs or spacing. I mean, really? It's hard to read a story that's just a big blob of words on the screen. Without paragraphs or spacing it's really easy to lose your place and reread a sentence by mistake. Some people make up an excuse saying that their updating on their iTouch or something- I don't care. If you want you're story to be good, fix it when you get back home!

[Oh God... I felt like a retard writing this. Props. to you if you actually read that. ]

3. Don't overuse punctuation either. If you were an awesome author, I think you could portray the characters feelings without being too excessive.

Remember:

Nobody likes to read something confusing, really. People like to read things that are easy to understand. Be neat! If you want to be a good writer, be very neat.