Even today, many homebrewers are afraid to keep the beer in primary for too long, for fear of the dreaded "yeast autolysis", which smells and tastes like burnt matches and/or rubber. I think that's the main reason "secondary" was popularized, once upon a time. While autolysis is a very real phenomenon, in the homebrew setting I have found that it takes at least 6-7 weeks in primary before this is possible, and even then I would say the risk is low to moderate, i.e., it isn't always a for-sure thing right at the 6 or 7 week mark. It might take many months, or might even never happen at all. SO... if you are an extremely patient or lazy brewer like I am, you might want to consider moving your beer out of primary at about the 6-week mark, just to be on the safe side with respect to autolysis. But other than that, yeah....
I don't usually secondary anymore. As a guy who bottles everything -- not a kegger -- I am still toying with the idea of whether it helps reduce sediment in the bottle. I mean, since on bottling day some sediment inevitably gets transferred over to the bottling bucket, I do find some benefit in inserting a secondary step to eliminate the vast majority of the trub before bottling day. But, on the other hand, like I said, I am also pretty damned lazy, and also a bit absent-minded..... so like for my last batch, I just moved the beer from primary to bottling bucket, did not do a secondary. Maybe I should have, if I wanted a really crystal clear beer... which actually, yeah now I wish I would have. But I forgot. Oh well. Just be gentle handling the bottles, and always leave the last half inch of beer in the bottle, problem solved for the most part. For those of you who keg.... I'm not sure why you even read this far, I sure type a lot.