My late father's former union organised and paid for legal action against his employer due to the life-threatening condition he developed due to their working conditions. He would have been pretty powerless otherwise (I'd actually previously engaged another legal firm for him myself who wrongly said his case was hopeless and told us we couldn't proceed).
That said, at the top level the union bosses are all part of the sham 'game' with government. It was all orchestrated in the 70s and 80s to de-power the working men (force a crisis that only affected the people - not the fat cats - and close the coal mines etc).
Exactly the same is happening now (except the unions are even more of a puppet, thanks to Blair and successors taking Maggie's baton) . Unless you think that nurses strikes etc at a time when elderly folk are being told they can't heat and eat is a coincidence - all because of Putin, climate change, and post-covid supply issues, of course
Basically the unions are just another player in the grander scheme of things, but (the way they make them so, otherwise no-one would join) as an individual they can be priceless.