This is in fact a very useful planning strategy. Whenever you build sensors that are smaller than the maximum of 2.5kt, you are kind of wasting your nation's current tech potential. If you already have a moderately sized fleet of combat vessels, it makes sense to start to delegate senor jobs to specialized ships. A 7kt destroyer could barely handle such a maximized sensor herein, so having one for missiles, one for ships and one for thermal maybe can be really fortunate in a fleet. However, you will have to find out a ratio of combat vessels vs. sensor supplement that makes sense (I guess somewhere between 6:1 and 10:1), because escorting for example mere 3 combat ships with full 3 sensor specialists is wasteful.
Aside from the obvious range advantage, some more Pro's and Contra's of this strategy:
+ With the sensor jobs taking care of elsewhere, you are now free to designate the full mission tonnage of any real combatant towards weapon systems only. This is a real advantage to missile ships in particular, who live of on getting sufficient salvo densities. Generally, higher specialization seems to be an advantage in any case too, which is the reason why huge capital ships normally stand little chance against equally sized but more specialized destroyer fleets. So further forwarding this can only be good.
+ Reduced need for a third active sensor. Facs get deployed by different opponents and usually dodge the regular ship sensors to a good degree - ..good enough to sneak under your maximum missile range. With an active ship sensor of this magnitude however, even the reduced ranges can be good enough to spot them at the tip of the spear. (still depends on tech level though)
- Without sensor redundancy you can quickly get blinded by some lucky random targeting. This might fade as your fleet grows larger and you can add more of every type of sensor ship, or you might have a fallback.
- Sensor research can be quite expensive itself, so "unleashing current tech potential" will actually take away from growing your potential further to the next generation. It is not too much in my opinion, but I can see why some people prefer a middle ground, especially early on where tech tends to grow rather quickly. - Nonsense to go big here and throw it away just 3 years later.
- Having a single huge component results in having a high chance of extreme maintenance need, so these specialized sensor ships will likely need extra care and supply (at least when kept at destroyer size). If you play with tanker fleets anyway though, it should not be an issue to grant some MSP supply ship to that, so the life time difference between the sensor ships and the regular ones can be evened out.
Instead of complete specialization, most people seem to go a middle way though, where they have either a destroyer leader (actual hull classification in the designer window btw.), or even a bigger cruiser sized ship as a command vessel that mainly consists of flag bridge and large sensors. In this case they seem to combine all the different sensors into one vessel, which however again leads to not realizing full potential, but at least the real combatants can still unleash their full mission tonnage towards weaponry.