well, where to start. your brothers comment i guess. it is a pretty good answer
really though, the reason people over clock may vary. generally to get better performance from your computer. some just because they like tinkering on them. i would equate it to working on a car. you get better parts to obtain better performance.
with overclocking safe and stable are the ideal goals. really though, it is at your own risk. so tred lightly. steps to include are read, a lot! then read some more. taking small steps, trial and error, and reading are the only way you will achieve a safe and stable over clock.
the practical uses included, anything you do on your computer. overclocking helps get it done faster. the loading, response, and running of games, apps, and what ever it is you use your computer for, generally increase.
why so much fuss?? its all the rage bro! again, the people "fussing" about it are people that like to tinker, or want better performance from the computer. generally the performance. games for instance, you yeild a greater frame rate(fps) with increased performance. so when your shooting zombies, or hugging ponies there isnt any lag or general skipping. hate the long load times? well getting more, better, or increasing the speed of your memory can shorten the loading times.
these may not be the best answers. i hope it is a start for you. god speed...
...and of course post back with any other questions!