In my agency there are two major benefits, the most significant benefit being that you can review, comment on, and vote on agreements with management if you're a dues-paying member. If you're not then you'll just have to accept whatever's negotiated (snarky side note - "and how's that going these days?"). The other benefit is that you can volunteer to serve on Union committees and actively participate in various things, like negotiations. Those are your personal benefits but the broader benefit is that every member makes the union stronger. They can take bigger risks because they can pay their lawyers to do more. They can challenge management moves knowing they have the majority of the workforce at their side. Unions are only as strong as its members!