Why go
A cab can turn a complicated cross-borough trip into a single ride, especially with bags or a group. Yellow taxis are closely associated with Manhattan, while other licensed taxi and car-service options extend the choice into the outer boroughs. The important decision is not speed alone: road traffic can make a rail or ferry connection the better option.
The full story
Taxis solve a different problem from the subway. They are most useful when luggage, weather, limited mobility, or a late journey makes transfers undesirable. In Manhattan, yellow taxis are a familiar part of the street; other licensed services can be more useful in the outer boroughs, where a yellow cab may be harder to find. The city also has car services arranged in advance, which can make sense for an airport trip or a larger group. Traffic, however, is an unavoidable trade-off: a direct ride through Manhattan can still be slow when streets are congested. Use a licensed service, confirm the current fare method before departure, and compare the travel time with rail or ferry options when the route crosses the city.