I've been using roles in D&D since 2011. Here's a write-up of them I did in 2013. These days I've also added the "Note-Taker" and "Monster Wrangler" roles. Here's how the roles fit into my overland travel procedure.The adventure phase travel rules from The One Ring roleplaying game give specific roles to PCs during overland travel: navigator, scout, hunter, watch. Random encounters are based on or modified by PC checks for these roles. Something similar could be done for DnD campaigns. Ideally, roles should provide PCs with interesting choices during travel.