Yes. I was a union member all my working life, and ended up as an elected official (unpaid, but with time in lieu) negotiating on behalf of members. There are a number of reasons for joining -
Job insurance Your employer is a big organisation with money and professional expertise. As a single employee you have neither. That means that the negotiating power between you and your employer is highly skewed. That doesn't matter so much as long as everything is going well, but could be the difference between keeping your job and losing it, or a significant sum of money, if things go wrong.
Terms and conditions Your working practices, working hours, benefits and pay rises will all be negotiated with the union. You get the benefit of these even if you do not join, but if you do join you get an input into the union's negotiating position, you strengthen the union's bargaining power by adding to its membership as a percentage of the workforce and you avoid your colleagues seeing you as a freeloader.
Club benefits You get the financial advantages the union has negotiated for members, typically insurance, credit cards, shopping and holiday discounts, and you get the right to make suggestions as to further benefits the union can negotiate for its members.