The type of bullet is much more important than the weight. A 130 grain Barnes Triple Shock will retain nearly 100 percent of its weight. A 150 conventional jacketed bullet will probably retain around 50 to 60 percent of its weight. That means the Barnes goes in with 130 grains, and out with 129.9 grains. A 150 grain bullet designed to shed weight might come out (if it exits at all) with 80 or 90 grains left.
Really, in 95 percent of the cases it will not matter. Where it will matter is when you're taking a marginal shot at longer distances. Trying shooting through a bull elk lengthwise at 400 yards with a marginal bullet, and you'll probably wish you'd spent $1 more for a better bullet.