To explain let me tell you how I start exploring possible services or opportunities to join. I read a lot. I click on headlines that interest me. When I read a well written article (or a useful comment on an article) that provides good information and shows the writer knows where he/she is talking about I will click on their profile picture to learn more about that person. I do usually not click on cats, dogs, cartoons or celebrity pictures; I tend to think that a person who does not show his own picture has something to hide.
Sometimes there is a profile picture but the profile info is empty or only has a link. In that case I loose interest.
I am active on several networks. By reading and checking profiles I am able to separate to copy/paste posters from good content posters fast. So in live feeds I scan for familiar faces and I check out new posted articles (and their profiles in I think it was a good read).
In online business there are many people promoting the same opportunities and services. Than when I want to sign up for such a program or service or buy something, I prefer to do so from people that I feel are knowledgeable and have proven to be helpful in articles and comments. Rather than from Mr/Mrs Incognito who provides no other info than a link.
When you have no intention whatsoever to engage with other people to establish relationships it is a waste of time to join in my opinion.
You don’t need to write your life story on your profile. Just write some personal info about you, your interest and your business if you have one. On most profiles you can add one or more links to your main opportunities. Several networks also offer the possibility to ad tags for what you have to offer, your interests and what you are looking for your self. Either in the profile, in publications or both. By all means use them! It will help people find you better within that network and it is also better for SEO.
Many people join multiple networks. Using the same picture everywhere helps for personal branding and recognition. Establishing business relationships and connections will take time. Setting up a decent profile is a crucial first step.
Related topic: Social Media, which ones to join and how many?