The grid system allows you to choose how deep or how little you want to use it. You will be able to do the basic actions of the game via the old school text way like you are used to, and behind the scenes the game will act as if you used the map.  For example, if you fly into Philly, then purchase drugs, travel to another district, sell drugs, do a few crimes then fly out later - these actions are being generated and completed on the grid behind the scenes. It will do the shortest path from the airport to the dealer you chose, generate the appropriate traffic, move to the next dealer in another district, sell those drugs, generate that traffic, and so on.  There are some tiny advantages to going the extra mile but the old school text way will still get the job done too.

A lot of the new businesses coming online serve either functional uses, or as income generators.  Every area and every NPC will keep a record of your interactions with it and react accordingly.  Always fair with a dealer who sets up shop on your property? - They will be back more often.  Get greedy and demand a higher cut?  Pfft, they will move on and drop you like a bad habit. In the beginning until everyone is comfortable how this works, things that hurt your relationship is a temporary thing.... Crank up the greed too much and they walk, but they will forget about it sooner than later. As time goes on though, if you get too greedy, they may hold a grudge longer and reluctantly do business with you without the benefit of friendly discounts.  You'll have to trial and error your way to figure out how to maximize profits without being greedy to the point you piss them off and they walk.

The grid system has pre-existing population data, however, as users use it, it will track how users move about and utilize different parts of it.  The NPCs will start to mimic player movements and population will slowly be influenced by user activity.  Why does this matter? A businesses value relies on immediate local population and foot traffic.

So when selecting your properties, here are some things to look out for.

Higher than average population.
There is a toggle on the overview map that shows you a heatmap of the population.  Blue colors are areas of low population, all the way up to red colors which are high population.  High population naturally drives more business in that immediate vicinity. 

Higher than average foot traffic by users.
People land at the airport and travel to different parts of the city, these areas will experience a lot more foot traffic than, say, a few random places on the very outskirts of the map with very little surrounding POIs.

Adjacent properties.
Properties that sit side by side open up the possibility of future expansions that single properties may not be able to advantage of. 

Nearby properties.
Owning a larger portion of an area than others gives you some extra opportunities.

Aligned properties.
While ownership of properties is not disclosed on the map, there are advantages of owning properties near those who are in your inner circle and you may currently work with, or under future accounts.

Denial properties.
Even if you choose not to build up a property, owning one in a strategic area in another city takes it out of the hands of your opponents and may set you up better on future accounts.

Property Types.
You can view a property and how it is currently set up.  Some are already perfect for long term investments with tenants spitting out rent checks on the regular.  Some are great properties that are currently underutilized - building up, or tearing down to change the property type to suit the area and your needs can really line things up for your future. Some businesses are perfectly A-OK being out in the middle of nowhere.  Your stash house where you store things over the long term doesn't really benefit as much by being right on top of the airport, but a location that is drug dealer friendly close to a transportation hub would benefit greatly.