You're an engineer at Nortel, Ericsson, Lucent, etc.

How can LinkedIn help you?

1. Headhunters. Would headhunters help you more if they see that you have over 50 connections. Probably. That's because they see more word-of-mouth potential. (If they help you, you might tell your 50 connections about them).
2. Potential employers. Should you let potential employers know about your LinkedIn profile? Difficult to answer. Yes, if you want to show them that you have only one resume version, and it is viewable on LinkedIn. Indeed, many people use different resume versions to make them fit the job they're applying for, and that might turn off employers, who view it as a lack of professional integrity. Also, the fact that you show your resume on LinkedIn means you have nothing to hide and that all your information (job titles, dates, etc.) are accurate (nobody would dare to lie on LinkedIn, since one's connections can see one's resume).
3. Your profile. LinkedIn forces you to clarify your Unique Professional Value (UPV) as well as your career objective. It's not enough to put down "engineering position" as a career objective. It should be more passionate, focused and unique. Your UPV also should be unique, and be supported by all your previous professional experiences.