Here’s a common scenario: You have an array of small components. Maybe some SOT23 transistors or a set of LEDs. On one side, you have wires and chips and stuff hooked up all over the place. On the other side, you have a ground plane.
The easy route would just plop the grounded pad of the part right on the ground plane. You would get better heatsinking if needed. You get a much more direct path to ground. It would be quicker to lay out.
But — and there’s almost always a “but” to such questions — you could get tombstoning. Especially if the parts are 0402s or smaller. You would also likely have soldering problems because the plane will act like a heatsink and may keep the solder paste from melting.
If you really need to, you could do the pad directly on plane thing, but you’d probably have to hand retouch each connection on the big pad and maybe rework tombstoned or crooked parts.
Much better would be to do something like the image on the right. You could also use thermal pads in the plane. With really small parts though, you might still be opening yourself up to soldering problems because of the heatsinking of the plane. The thermal pads would typically have three connections to the plane in a setup like this and that could still be an unequal amount of copper connecting on one side vs the other. You generally want the same amount of copper on both sides of the small parts.
You could also just run the eight traces straight to the plane. How would you approach this seemingly simple but surprisingly error-prone layout?
You’ll take the left road and I’ll take the right road
And I’ll be in reflow before you