Here's one event with at least two very different uses. The first is to do literally what the title suggests, and make a return trip to a mission you've already completed. Some missions have game text that tailor so wonderfully to your deck, it's a shame you can only complete them once. With Return Trip, once is never enough. You can complete Destroy Minor Goa'uld again to destroy another adversary, or restack your top mission again with Research Advanced Races, or repeat any other mission that's your personal favorite. For this sort of use, Return Trip is particularly good to set up your second mission in a turn, when you're often down a lot of characters (who were stopped in the first mission), but still have power. Why go blindly to your mission pile and hope for a mission that fits your remaining skills when you could use Return Trip to put the right mission on top of the pile?

The second approach to Return Trip is to use it like the game text of Vala Mal Doran, Con Artist -- as a way of "upgrading" your glyphs. While at first it may not seem like too great a deal to switch a 1 experience mission for something potentially higher when that 1 experience mission is going right back on top of your mission pile, timing is everything. Sometimes in a game, you have the power to continue to additional missions, even though you know you lack the ready characters to complete them. If you play Return Trip at that kind of moment to "upgrade" a low-experience glyph, you can then continue to your recently-stacked mission right away, on that same turn. You aren't really planning to go after that mission, you're just getting it off the top of your mission pile now so that next turn (when all your characters are ready again) you can complete a mission you're really after.

Whichever approach you take, Return Trip can throw a surprising curve ball at your opponent.