Like most elements of modern life, computer use is about balance. I use a PC every day for work but steer clear of in on evening and weekends, preferring to go outside, spend time with my family and generally do other things. Some people take things too far, just like some do with eating, boozing, shopping, watching TV or playing video games and just about anything else.
Being online makes us relatively anonymous and therefore more able to express ourselves without fear of repercussion, something that most of us would be unwilling to do in "the real world".
PC use has a great deal to answer for and I have observed a marked decline in spelling, grammar, and handwriting in people I know are heavy "users" as well as a general lack of interpersonal skills.
Everything in moderation is what I say.
The straight answer to your question would be that computers were invented to perform complex calcualtions rapidly, accurately and repeatably and were first used in processes such as codebreaking, census taking and bookkeeping.