If building your network is one of your business goals, then getting back in touch with former colleagues or supervisors might be part of that strategy. Often a previous co-worker can help with finding work, or an old boss can provide a good reference.
But when the working-together period was a long time ago, you may hesitate to reach out. In an environment where people make frequent job changes, it’s easy to lose touch. But that doesn’t mean you should write people off,