There is really no trimming needed on a brisket if you choose to, the fat will easily scrape off once cooked or can be easily trimmed off on a properly cooked brisket. There is really no right or wrong way to trim a brisket either, some trim nothing, some trim the hard, thick areas of fat, some trim like I do. I trim everything off the top and sides, leave the bottom alone for the most part except for those areas that I can tell are large, mass deposits of fat, I'll trim those off with the intention of getting the bottom layer of fat uniform in thickness, 1/4" or so. I also trim the heavy part between the flat and point out and either completely separate the 2 muscles or leave them connected by just a bit of the bottom layer of fat. This trim allows for more rub to hit more of the meats surface, which allows for more bark and more bark, means more better! It will also help the point cook a bit faster, so you can cut down on the extra 2 hours typically needed on the point end. It will still take longer to cook due to the internal fat, but taking off the insulation (excessive fat) really helps out. This trim really works well for some awesome burnt ends. I don't score the bottom layer, because I cook fat side down in my RF pit. I am using the bottom layer as insulation from the heat coming up from the RF plate. Here is a good watch on brisket trimming.