Yea each friendship you have might bring certain advantages. With Jacob, it's bringing his car to you with weapons/armor choices at discount prices.
My brother had some guy try to hit on Michelle during a date, so he tried to stick up for her. I think he had your early competence with the fight system because this guy was about to KO him when he pulled out a gun and shot him. Now Michelle won't take his phone calls at all! LMAO
While I don't see any perks to having Michelle as a girlfriend, if you lost her, don't worry there will be other ladies who do offer perks. If you have a saved game/autosave, you can go back to it if you wish.
Hint for Little Jacob:Cluckin' Bell
At the beginning of the game there will be VERY few icons on your map. I am 2 dozen missions in and now my map is filling out, BUT I am learning new stuff on almost every mission STILL.
Once you do the first sets of missions your map will have a host of new icons for you to explore.
Don't forget you can go to your cellphone menu/options/Turn story mode off. This will stop the phone calls and let you explore the city, pickup weapons, armor, health, and get any packages you want to get out of the way.
Then when you are ready for your next mission turn story mode on. That's so terrific, on some of the harder missions you need time to prepare and this works perfect for that.
If you get stuck or need to find the stunt jumps and map items this is a GREAT site, and as you discover stuff feel free to add it to our growing map:
Grand Theft Auto 'Hood: GTA Maps, Missions, Guides and News