I tend to have a distaste for left exits, but I can tolerate them as long as they're in one of the following situations:
1. The expressway ramp in question leads to another expressway. If the turning movement onto this ramp is more popular than the thru movement, I'd even call the choice of a left-hand ramp favorable, not just tolerable. This applies to onramps, too; if an onramp carries more traffic than the thru movement, there's no problem with putting it on the left (assuming the onramp is a pretty high speed since it carries the most traffic).
2. A relatively slow urban section of freeway with a high concentration of offramps has an offramp on the left, or a series of offramps on the left. I prefer left-hand offramps to left-hand onramps, because merging into the fast lane is a dangerous proposition, as mentioned by many others in the thread.
3. An offramp to an expressway or other highway that's just beginning. Junctions like these are just splits in the expressway, where it doesn't really matter which carriageway appears on the left.
4. Express lane ramps, especially to/from other express lanes.
Low-speed offramps and onramps appearing on the left should be highly discouraged.
I apply these policies to my Cities:Skylines cities as well
