If there is a location of importance that the players might visit, you ought to think of details for that place, that way, when the story takes you to that place, you already have a lot of info on it as a GM and you won't need to make up new stuff up. I wouldn't overdo it with the info, though, I usually give two or three paragraphs for each location, the regime they're under and their trading/landscape benefits. A huge info dump can only serve to put off potential players who look into your OOC. As for minor locations, I think it's good to mention them separately from the important stuff as interesting trivia about the world.
I would suggest it, yeah. If you think about an RP as an animal, the plot points would be some of its bones - sometimes not connected directly, but at all times surrounded by the flesh, which the players bring. Plot points help you create a skeleton for your RP which will then be filled by the players... and skeletons help you avoid boneless masses of flesh that RPs that aren't thoroughly imagined tend to become.
At least that's how I see it. I've found this method has worked for me, but I don't know about other GMs. I don't want to make it seem like I claim my method is the only true method that works