LinkedIn is useless...
Some people may want to get:
- a job
- a better job
- a very specific job in a specific industry
- a consulting contract with a specific company
Other people may want to give away:
- their experience and wisdom
- their professional expertise
- their political connections
Of course, the above does not preclude benefits that a person can get via serendipity.
But it's always better to have a clear goal, and LinkedIn doesn't seem different from any other tool: success depends on knowing what we want to achieve, and then using the tool specifically to achieve precisely that.