The purpose of language is to be understood, to get an idea from your thoughts to someone else's thoughts. You want to make that idea as clear as possible so the person you're talking to understands as closely as possible what you're trying to convey. Everything, from a declaration of emergency to a simple joke should be succinctly conveyed or the person you're talking to won't fully understand.
So, when I hear people mixing 'when' and 'whenever' up, I cringe. The two words have different meanings. 'When' means a particular place in time. 'When I was born.' 'When the saints go marching in.' A birthday is a particular point in time. The saints will go marching in at a specific point in the future. All the musty dates in history class are 'when'.
'Whenever' is a hypothetical or a series of points in time. 'Whenever she gets here.' 'Whenever we go out we end up at Starbucks.' Your friend is reliably unreliable so when she says she'll be there at eight, you might see her at eight or you might see her at eight-thirty-five, or even nine. You have that friend. If you don't, maybe you're that friend. ;) 'Whenever we go out we end up at Starbucks.' No matter what else you do together - shopping, freshman orientation, church, just walking around, whatever (another hypothetical or series of events) - you do the activity, then you go to Starbucks together before you go home.
'Whenever' can have consequences. Imagine a person going to HR to complain about a personal infraction. 'When he touched me' has very different connotations than 'whenever he touched me'. 'When' is a specific point in time, so the complainant can point to an exact moment of touching. So, 'We were in the file room when he touched me.' It might have been an accident because the file room is small and/or cluttered, or it was a one-time-only thing. 'Whenever' means it has happened more than once or twice. 'When we were on the elevator this morning, and when we were walking into the meeting yesterday afternoon, and several times when we were in the file room together, and a few times I've forgotten. It happens all the time.' That doesn't sound like an accidental touching, it sounds like it's on purpose. Which would you rather have someone say about you, 'when' or 'whenever'?