To understand that, we have to take a look at the history of Chess.
Chess has traditionally been characterized by quick exchanges and second to second gambits. You rarely had a boring moment during those plays. This is tactics. It wasn't until recently in the nineteen hundreds that you had more passive games with more careful setups and longer-term plays. They were positional.
Now cut back to 2017 and a younger TerribleTy has started to realize that pretty much all sparring matches can be sorted to one of two types. You had intense, continuous matches where at least one side never let up the heat, and you had more careful matches with slight foot movements to just subtly advance your position while simultaneously preparing yourself to do a turning kick.
I had just gotten into chess, so I thought it would be funny if I mentally named these two states 'tactical' matches for the former and 'positional' matches for the latter. Sorting these out in your head is immensely useful, as you can create custom strategies for each type of match.
Don't get me wrong, it's pretty much a spectrum, which hurts the usefulness a bit. A positional strategy will only get you so far when the match is two steps away from tactical, but it still allows you to think inside a structure, which is very useful starting out for beginners, and even for some advanced. Something very important to note is that aggression/offense and passive/defense are all on ENTIRELY different scales. Do NOT mistake a positional player for a defensive one. Do NOT mistake a passive player for a defensive one.
Some of the most aggressive and intense players I've ever meant were primarily positional. Some of the said players were aggressive, but they weren't even offensive, they were straight up defensive while still being aggressive. So, how do you utilize this system to the max?
Well, a good place to start is by watching matches online and writing down what type of match it is, along with how the players approached and how you yourself might've broken through someone's defense or something.
Sorting matches mentally as you fight is a good start too, as you can hone your technique and recognition given enough time.
Practically, if you know that this match is gonna be positional, then you can surprise someone by switching to tactical. Just don't go overboard or you risk the opponent taking advantage of a spot in your defense.
On the other hand, If you know it's going to be tactical, learn how to surprise your opponent using positional techniques. But be careful not to be trapped inside a mental box. If someone breaks out of the system and defies classification, better to do away with the system then let it distract you midway through a match. Thanks for reading!