It works very well for some purposes and people (mostly if you live in a well-populated area, and work in a central business district). It works very poorly for others.
I worked in downtown Chicago for the past 22 years, and lived in various suburbs. Taking public transportation (commuter rail, and later light rail (the L) ) was always feasible, as the train lines were built for bringing people from the surrounding areas into the central business district of downtown Chicago.
I just started a new job, in a different suburb from where I live. My suburb is served by the commuter rail line, as is the suburb where my new job is located. But, to take the train would be a nearly 3-hour door-to-door trip, as I’d have to take one train into downtown Chicago, then hop on a different train to head back out to a different suburb.
Alternately, I could take the public bus. According to the online trip planner which the bus authority has, it would require taking five different buses, and take 3 hours.
So, I now drive to work (a 35-minute, 20-mile drive).