You can do it that way if you prefer, but there's really no need if you develop the ability to freehand judge each step of the plunge until you reach your final depth, as controlled by the depth stop. So, for example, if you're using a 12 mm diameter cutter to create a rebate, housing, or trench that's, say 12 mm deep, set the depth stop to achieve this, and then take two to four small plunges to get to that depth. A useful guide is to aim to increase the cut depth by approximately the radius of the cutter, or a bit less. For a 12 mm diameter cutter aim to increase the depth of cut in roughly 6 mm increments, for a 6 mm cutter aim for roughly 3 mm plunges. However, you should also be guided by the amount of material you're taking away, and how hard this makes the router work, especially if you're working with large diameter cutters, because the larger the diameter of the cutter the greater is the risk of kickback, e.g., a 25 mm or 30 mm diameter cutter requires even greater caution and vigilance than perhaps a relatively small cutter.
To set the required cutter depth, zero the tip of the cutter by placing the switched off router's base on the material to be cut, plunge the non-rotating cutter to touch the surface of the material, and then trap something of known size between the stepped rotatable turret attached to the router base, and the adjustable depth stop, then lock the stop. For example, a 9 mm drill bit used this way will give you a 9 mm deep cut.
On a final note, for you to be asking such a question suggests very strongly to me that you have little or no experience using routers. They can cause significant injuries in inexperienced hands, and if my suspicions are correct I strongly suggest you seek guidance from an experienced and skilled user - be wary of what can be viewed about router use on places like youtube - there are a lot of clowns out there only too happy to demonstrate confidently to all and sundry their stupidity, incompetence, and fondness for dangerous router techniques. Slainte.
