Just last weekend I was removing a bolt that my 13mm 1/2" drive impact socket couldn't reach because it was too thick, the bolt head was too close to a flange. I switched to my 3/8" impact socket and it did the job. I could have switched to my chrome 1/2" drive socket and it would have done the job as well... or my 3/8" drive chrome 13mm socket.
Since it was exhaust work, stuck and rusty, (muffler hanger where it bolts onto the frame) I went with the 3/8" drive impact.
Point being, if I had no 3/8 impacts handy, I would be trying to bust a rusty bolt off using a chrome socket, and I'd rather it be a 6-point 1/2" drive chrome.
1. every single automotive job I've done I run into clearance issues, and
2. every single automotive job I've done there are rust and/or frozen fastener issues.
If you don't have these problems, you don't need as many options as I do.
I agree with Adam that 12 point 1/2" drive chrome sockets are handy. I'm not so sanguine on dumping 6 point 1/2" drive chrome sockets, even if you have impacts, because they are still thinner, and sometimes you need to bust a tough bolt with 1/2", 3 extensions and 2 u-joints and that nun-chuck on the impact is going to injure you when that mess comes apart. With a breaker bar I'll just skin my knuckles.