It's a retirement plan, but you buy stocks with it, instead of the govt just giving you an iou. Most big employers match what you put into it, up to a certain percent. Mine matches up to 6% of my gross pay. The main incentive, aside from the company match, is its buys stocks at pre tax dollars. It also grows tax free, until you take it out. Hopefully you retire one day, and start withdrawing from it when you're making less and will pay a lower tax bracket. The only drawback is you can't touch the money until retirement age, or you pay a heavy penalty to the govt. So as long as the stock market does well, your money is safe. Even if the market goes down, since your company matched what you paid in, it would have to drop 50% before you loose any money. I'm just nearing 52 now. I think you can start taking it out without penalty at 57 1/2 yrs old. So hopefully the market will still have value in 6 yrs. I'm not sure, but it may be 62 yrs old. Either way, I can't use it right now without taking the penalty. I've heard with penalty and taxes, you end up getting about 50%, which is what you put in it. I look at it as just another form of prepping.
