In the past we have done a fair amount on one ways to Europe because we were not sure of when we would be returning or from where.
There are a few airlines that offer good one way fares IF they serve your area.
We have also been very fortunate snagging one way tickets on BA through consolidators. We have had two one way flights to Istanbul that were priced at half the price of the best return that we could find.
We also shop by European gateway. We can fly to London or Paris, and then a LC ticket to get to Athens, Cyprus, Italy at a much more attractive total fare.
It takes a little work. Since retiring I do this on a regular basis. We are going to Morocco next week. It was far less expensive for us to fly to Montreal on a single ticket and then pick up a fare to Casablanca. On the same airline no less.
Last year our one way fare on TAP to Toronto-Madeira (via Lisbon) was less expensive than a one way to Lisbon. Coming home five weeks later, our flight on Transat from Faro, Portugal to Toronto had a base fare of $300CAD ($225USD). The best part....it eliminated the need to travel back to or fly from Lisbon, or buy a connecting TAP flight from.through Lisbon at a considerably higher price.
It does take some shopping though but my time is cheap.