No, all shapes (tabs, slots, or otherwise) will only need one kerf adjustment (with a minor caveat, which I’ll explain below). This tutorial shows a quick, easy, and (most importantly) correct way to create a kerf-compensating offset.
The image smcgathyfay showed had a design flaw. The flaw was that the two sides of the box were touching each other. It’s as if the person who created that box design was ignoring or unaware that a kerf would be created when the two pieces were cut apart. With a properly-made design (one that has allowances for kerf in all directions) only one adjustment is needed, the one @Jules shows in the OP.
OK, the small caveat…
Yes, the beam/spot of the laser has a shape. That shape is not square and it does not get altered to conform to the object you’re cutting. For all intents and purposes the shape of the laser beam is round, just as @palmercr said. The shape is a circle and the diameter of that circle, in the context of the Glowforge and this tutorial, is 0.2mm.
When that round beam cuts, it leaves a round hole.
When the round beam changes direction (goes around a corner) it leaves a radius equal to the radius of the beam. The radius of the beam in this example is 0.1mm. That means the radiuses left on the insides of the corners that are cut with this round beam will be 0.1mm.
Although this radius is very small and is hard to see, it does exist. Smcgathyfay is right that it basically doesn’t matter, but isn’t right about it not existing. That radius exists whether the laser changes direction at 90°, 45°, 18°, 179.999°… basically any time the laser changes direction at a corner, a radius will be present on the inside of that corner.
Back to the caveat… Imagine you are cutting an acute angle. This angle is very narrow and very long. You’re cutting the inside of this angle. As you get closer and closer to the point of this angle the distance between the two lines will get smaller and smaller. Basic arithmetic tells us that, at some point, the distance between these two lines will be smaller than the diameter of the laser beam. That is the point where the laser will change direction. And, since we know the laser has a shape, and we know that that shape is roughly round, a radius will be present on the inside of the corner where the laser changes direction. The corner will not be sharp. There will be a radius. This is a fact. The area between the radius and the actual point of the angle you’re trying to cut will not be cut.
This area, however small and potentially insignificant, does exist and it’s important to be aware of these things. If the tolerances of the part you’re making are tight enough that these uncut areas will not be acceptable, you will have to find a different way to cut them. Perhaps a wire EDM may be an option.
So, again, the method shown in this tutorial will work for ALL shapes, regardless of what you call them, as long as the very small radiuses that are left on the insides of corners do not affect your design.
Sorry to repeat myself so much and be so long winded, but I’m trying to nip any further misinformation in the bud.
OK, one more caveat: this information doesn’t account for laser power variations, acts of god, material variations, presence of explosive material, earthquakes, gravity waves, sabotage, uneven cutting bed, temperature fluctuations, or power outages.