Occasionally in YC founder circles a new founder will raise a bunch of money and then ask something like "What's the best way to invest all the money our company just raised?"
The responses are always along the lines of "Your startup is already risky. Don't innovate in areas of your business where the status quo is known to work. Innovate your product + technology, don't be innovative with your company's finances, HR, etc"
That advice always stuck with me. It just makes a lot of sense to do things in the most boring way possible, except where it matters (your competitive advantage <-- that's where you innovate, that's where you set yourself apart)
Running a startup is distracting enough. Doing things non-standard just adds to the list of distractions that you don't need as a founder.
The return won't be much but it's better than letting the cash sit idle and evaporate due to inflation
If you have a huge chunk of change sitting around, you've raised too much or too early, and you've successfully diluted yourself for zero reason.
If you actually had a reason to raise a lot of money, you'd do with the money what you promised the investors (who gave you the money) you would.
I've raised before. I raised what I needed. Not a penny more because I didn't need the money.