It's 'take greater combined power against the corporation you work for' (and in things like representation of your industry before government) or stand on your own as you do now.
I don't understand how it's possible to lose?
You can even wimp out at the first call for solidarity of you want to.
In my current role there are 3 unions that are well represented in the work place, I chose one that seems best to represent my interests and that has members in industries I might move in to.
Benefits for me are currently advice seminars on career progression and work related issues (pensions!), and annual pay negotiations (which are quite weak, pressing for inflationary pay rises).