Why go
Driving can make sense for destinations beyond dense transit corridors or for a trip that begins outside the city, but it is a poor default for Manhattan sightseeing. Parking is the main constraint, not just traffic. A visitor who needs a car should decide on a garage or legal parking plan before arriving, then use walking and transit for the central part of the day.
The full story
New York's density turns driving into a planning task. Traffic can be heavy, parking near crowded areas is limited, and the city's street rules require close attention. Manhattan garages may not be obvious from the street, while curb regulations can change by time and location for cleaning and traffic management. For many visitors, the better approach is to leave the car at a commuter-rail station or ferry terminal and continue into the city by transit. A car becomes more useful in parts of the outer boroughs or for destinations not served well by rail. If driving is necessary, check parking availability, current restrictions, and the exact address in advance. Do not treat curb space as a casual option; use posted signs and official city guidance as the final authority.