While traditions are far from perfect, they help get us started as we figure out how to do everything from celebrating life to mourning death. Life cycle events are stressful enough on their own, without needing to negotiate how to best host a gathering for the occasion. Cultural and religious traditions help alleviate the need to make so many decisions. They also give us confidence that we're not forgetting anything important or obvious when we're overwhelmed by emotion and seeing loved ones.
In many ways, traditions and habits play similar roles. Instead of spending conscious energy deciding how to do day-to-day tasks from scratch, we start to delegate things to our subconscious, so they can be done on autopilot. Similarly, traditions help us focus on processing our emotions by helping to minimize the amount of time spent thinking about logistics.