I agree that it will be near impossible to overcontribute to an HSA. It is easily the best retirement vehicle available, which is why maxing it is listed as the 3rd priority in the
Investment Order post, after getting your match and paying down high interest debts.
You get:
1. Immediate income tax savings on contributions. 401k-like.
2. Immediate FICA tax savings on contributions, if you are contributing through employer cafeteria plan. Unique to HSA.
3. Tax-free growth. No taxes on interest, dividends, or capital gains. Roth-like.
4. Tax-free withdrawal for medical expenses, at any age. Unique
5. Tax-free, penalty-free withdrawal for Medicare premiums. Unique.
6. Penalty-free withdrawal after age 65. You still pay tax on it at your marginal rate, making this account functionally like a 401k or tIRA (except for age 59.5 vs 65).
7. No mimimum distributions requirements. As you age through retirement, you are free to withdrawal or let compound as you please.
I want to highlight benefit #5. Once you are on medicare, you are allowed to pay your medicare premiums with your HSA,
tax-free. Meaning, at a time when people are drawing down from their retirement accounts to pay for expenses, what you draw from you HSA will not be added to your MAGI, keeping your overall tax bill lower.
We have been on a HDHP since 2016, so for my family of 4, our HSA balance is about 24k. Most of it is invested in a total stock market index, though there is some cash sitting idle. I have my account set on a sweep when the cash reaches a threshold, so there is some inefficiency built in there.
In terms of withdrawal strategy, initially I was keeping all my receipts by scanning. But we have been incredibly blessed with good health in my family, so my receipts were all dinky bills <$100 or co-pays <$30. For these amounts, it seemed like a hassle to scan them all in, save them in a folder on my computer, and remember to back the files up. So I just take the withdrawal for these small receipts as they come now. Should a larger bill come in the future, I will probably go back to scanning them.