I will start by saying that I am moving more towards the full PhotoMechanic solution although it isn't happening nearly as quickly as I would like to. But again, I also deal in large numbers of images...I usually come home from a game with 500 or more images and there are times when I am shooting multiple games a day and even more frequently multiple games a week...
While I have been using LightRoom and PhotoMechanic, I still layout my images in a folder structure that I've been using for many years. Below the main folder, I have folders for each year, below that I begin the categories...these tend to be fairly generic such as the US State where the images were taken or Sports or .... and below that (using Sports as an example) it gets broken down further to individual sports (football, basketball, baseball, etc.) and then to specific games. Same goes for the State such as Virginia / Wildlife / Deer or something like that as I extend the folder structure downward. The specific game folder has all the images for that game. I actually maintain this same structure across the external drives using a large drive as backup with multiple years and smaller external drives that will each have about 2 years of images before archiving. So one has 2014 and 2015 while a separate has 2013 and 2014. Yet another separate external drive has 2015 and 2016 (still building, of course).
The one other difference is that under each year I have other folders for various projects, but I guess the other real key folder per year is the Save folder. Beneath Save is a similar folder structure to that described above but those folders contain only images that I have exported from LightRoom for publication to web or for other uses. Is it necessary? No, I could put the exported JPEGS in a variety of locations, but it works for me and I know where to find what I want when I need it. I also use the LightRoom keywords and am hoping to expand that use as I move forward to make what is a relatively easy search even easier down the road. Once images are processed and exported and the original folders / files are backed up to the other drives, they get removed from my internal drive so I always have space for the next sets of images. Speaking of which, I need to make sure everything is backed up and cleaned up since I have quite a bit of shooting this weekend!