Set for Life question: using Roth as savings location

[Shawn Q.]

I just finished @Scott Trench's Set for Life (as you can no doubt tell from how often I reference it) and I had a thought/question I'd like to put to everyone. What do you think about using a Roth IRA as a component of the savings vehicle for the $25K-$100K initial steps? Any of your contributions can be withdrawn without penalty, the money would have an opportunity to grow, and there would be a tax advantage to your contribution. I know the limits are fairly low per year, but the rest of your savings could go elsewhere.

As long as I'm aware of and accept the risk, is there a downside to doing this I'm not considering?