Especially sex together.
There's always KY in the shower, or "Mommy needs 10 more minutes of sleep, so go pour yourselves some cereal" on a weekend morning.
But, sometimes you just want to actually touch your partner, and your spouse has to go to bed before the kids because he works at WTF o'clock in the morning, so maybe you try a quickie of some kind while the kids are distracted, but then the dogs start fighting, or the kids do, or your mom--who lives in your basement--comes upstairs for something, so you pause your ministrations to your spouse's pleasure and go take care of it. By the time you're done, the kids may as well go to bed. It is amazing how long it can take them to brush their teeth, wash up, pee and go to bed. You think it's a ten minute job, but if you're lucky, your spouse is still awake 30-45 minutes later.
Pro tip #1: read a book that makes you hot and ready to go when you know you're going to have 10 minutes, and probably only ten minutes. This reading can be done while you're watching the same kid's show for the 12th time so that when hubby gets out of the shower, you only need 10 minutes to get off because you've taken care of the foreplay.
"Keep watching kids. Mommy's going to go help Daddy with some laundry."