Do I need to roast walnuts before adding them to a salad?
You don't need to, but toasting will amplify their flavor and give them a little snap. So if you have time, go for it, and if not, don't worry for a second!
No. BUT.... Imho toasting any nuts enhances the flavor greatly and adds wonderful dimension when used as an ingredient in any dish.
Totally agree with the above wisdom. No 'need' but the flavor will be much deeper and the texture much less like pencil erasers if you do. Preheat oven to 350 degrees. Spread nuts out on a baking sheet lined with parchment. Set a timer for 10 minutes. Open the oven and sniff for scent. Nuts are done when very fragrant. Adjust time upwards as needed.