>What are the ways to discipline oneself in using cellphones or Internet apps, especially in texting/chatting?
Let your parents confiscate it. :| As a less drastic measure I suggest turn off the notifications in the groups you are part of. Turn off auto downloading of images and videos too. Find another hobby like playing sudoku, read a book, draw something, if you can go out talk a walk etc.
>How can texting/chatting be helpful?
Share info about class assignments or other projects, home work help, sending other userful information/quick messages to each other. My family and colleagues also use what's up etc to send snap shots of necessary documents/pages from a book for reference to each other sometimes.
>What are its negative effects when used excessively?
#You may send something really stupid on a momentary whim that you come to regret later.
# Your socialization with real people becomes less and less and you are sucked in to talking to relative strangers on internet more. Just because you are talking to them too much and sharing more personal stuff to your actual friends and family you believe them to be closer.
First problem is even if they are genuine, if you need actual help they have very limited means to help you. Most can only listen to you.
Second one is they can be real jerks and you will be in trouble because you shared too much with a person you didn't know.
# You are so involved in replying latest random chat that you are late for school/work/losing sleep- this is the last thing you do before sleep and first thing when you wake up- find your mobile and read messages. And then you realize you are depressed that your virtual friends didn't post thumbs up emotes to the funny dog video you posted . Real trouble. Or you may find that your friends have been gossiping and you are the topic and then you end up making a thread in ND how chat groups are back stabbers...