I haven’t done a will in a coon’s age, but the way you’re describing it, Mama Zappa, isn’t the ideal way to go.
First things first: the spousal exemption is for any and all, property, including cash, so you can leave everything to your spouse and your estate will pay no tax, period. However, that wastes your use of your own exemption.
If the amount of personal assets you have exceeds the exemption amount, what you want to do is maximize the use of that exemption with some fancy lawyer-language. You don’t have to have a dollar amount in your will, or even a percentage. All you need is language along the lines of, “I leave to my spouse the largest possible amount that will result in the maximized use of my unified exemption” (something like that, don’t have the exact language at my fingertips). So, if the exemption amount is $5 million, but your estate is $8 million, that language passes $3 million to your spouse, tax-free, and $5 million to your other heirs, tax-free.
Putting in language like that, rather than a percentage or dollar figure, also makes your will immune to fluctuations in the exemption amount, so you won’t have to rewrite it every time Congress fiddles with things.
Our wills do say something like you describe, vs. a specific amount. My example of how this saves taxes may not be the best (given what you and others have said about passing money free and clear onto the spouse). I haven’t looked at our wills in over 10 years (no need since we haven’t needed to revise them). Now you’ve got me curious, however.
The rest of the estate, rather than going directly to the heirs, goes into a trust fund. The trust fund is available to the spouse during his/her lifetime - so s/he has access to the funds if needed. Then when s/he shuffles off, the rest is distributed to the heirs.