More realistic amounts of traffic on roads. More vehicles in urban areas at peak hours.
Less traffic in the country and desert areas, especially at night...

Also more pedestrians in the city around shops and commercial areas during daytimes
Gang members and drug dealers more common at night, less in the mornings and until afternoon

Police hardly ever walk around alone at night or in gang territories

v1.1 update:
i: Increased traffic in gangland areas in the a.m
ii: Increased traffic in upmarket residential areas in the p.m (the SA map defined the L.V strip south as residential so the traffic there was too quiet)
iii: Included a stream config file for better vehicle spawn distribution, vehicle and memory limits.

Super simple installation: two files to replace.