Guards can be either supine (on your back) or seated.
A supine guard is where you’re lying on your back. Examples include closed guard and de la Riva guard.
A seated guard is where you’re sitting upright. Examples include instep/shin-to-shin guard and butterfly guard (if you’re playing it right).
So, how does understanding this difference help us?
A lot of gi-based guards involve getting your grips and “falling back” into a supine guard. Think of the situation where you get a solid collar and/or sleeve configuration and then sit back into de la Riva guard, spider guard, or something similar. This approach of falling back into a supine guard only works because your gi grips are so powerful. If you were to try this in no-gi, you’d probably get your guard passed.
Imagine doing this in no-gi. You’d fall to your back into a supine guard, but any grips you have – likely on uke’s wrists – are probably not strong enough to sustain. This means you’ll likely wind up in the headquarters position on the bottom, where the top guy has one leg in and one leg out. And this means you’ll likely get passed.
There are a few situations where supine guards can work in no-gi, such as X guard and deep half guard. These work because you’re underneath your opponent and have strong control of their legs. You may not have gi grips, but the leg control is strong enough that you can sustain the position.
The moral of the story is, supine guards only work if you have strong enough grips to sustain the position. And because of this grip limitation, some supine guards are best suited for the gi.