I've never been in a union and have no intentions of joining one now.

I'm paid more than than the award, I get away with working short days, taking time off whenever I feel I need it and often working a little slower than I probably should, and I'm sure that there are other people that wouldn't last in a job if they did the same, but after almost 15 years, my employer seems to think that I'm valuable enough to let me get away with these things.

How would being a member of a union benefit me?