There was a post a few months ago about how software development should be a profession and we should have a strong professional association to help represent our interests. To help prevent things like this amazon case.
As one example, my wife spent three or four years without even having a collective agreement; their old one had expired, and the union hadn't bothered to/gotten around to/nailed down an agreement with the employer. Literally their biggest responsibility, and they were years late.
What they did do, however, was send out a mass e-mail to union members encouraging them not to participate in Ugly Sweater Day, because it could hurt people's feelings (literally, their concern was that people's feelings could be hurt), and other equally worthless wastes of time. Behaviour like that makes me wonder what these people actually do with union dues.
That said, there are also huge benefits; for example, there have been a few cases where people we know have been chosen to interview for a position, only to be told suddenly that the position was no longer being interviewed for – and then finding out that someone with less seniority and less experience was offered the job. Not saying our friend should have been given the position, but they didn't even interview her for it.
On top of that, there's the generic benefits of a union environment: more vacation, less nepotism, pension, and – my personal favourite – as long as you show up to work every day and do your job, your salary will increase (more than the legal minimum), your vacation will increase (more than the legal minimum), your pension will keep going up, and eventually you can retire.
So it's kind of a mixed bag. In cases of large, faceless bureaucracies it can help significantly by preventing people from being promoted who don't deserve it, just because they're friends with the boss/interviewed well/bribed someone/etc. On the other hand, large unions are basically another giant, faceless bureaucracy which purports to be on your side but typically operates under its own agenda, and in many cases, appears anti-employer for no reason other than spite.
Union Pros: Job safety, real cost of living increases, pension/retirement opportunity, some protection from unfair hiring/promotion practices.
Union Cons: Silly emails?
Job safety is good, but it does protect incompetents as well. That becomes a poor situation for everyone but the incompetent.