I don't think there is a single answer to this question.
The only thing you can really do consistently is figure out where your opponent is and what they're building.
The speed of the dot on radar should indicate which unit it is (or at least which type AKA raider if fast). A few raiders of your own walking along the edge of the range of enemy turrets should get vision on units being built and if there is an army massing somewhere.
With experience you can tell if you can repel what your opponent is building and can afford to take more risk expanding without protection, or if you need to stick with what you have and put up a few turrets.
Without that knowledge, you're flipping a coin. If you're expanding slowly and putting down turrets deep into your territory while your opponent is expanding naked, they're likely to out eco you and drown you in units. Then you'll watch the replay and hate yourself for not raiding and building too much static defense.
If you're expanding naked and your opponent is making a good amount of units, all the metal you spend in mex will get lost before they make cost. You'll watch the replay and tell yourself you were far too reckless.
But if you see what they do, you can use that information to your advantage.