What is the danger in cross contamination?
Whilst you'll probably be fine using the same knife and chopping board to prepare everything that's going in an "all in one" meal such as a stew, here's the reasons I have for never doing so:


It's a bad habit to get into. It's very easy to slip-up and forget that you're not making an "all in one" meal and thus chop some lettuce on a board you've already used for slicing raw bacon when making a salad, if most of the meals you make are "all in one" and you usually don't have to "worry" about cross-contamination
It doesn't take that long. Washing your chopping board down with hot soapy water and a clean sponge/scourer takes literally a few minutes, the same can be said for a knife. If you're pressed for time you could turn the board over and use a fresh knife. That assumes that the work surface was clean beforehand and the food being prepared on the "first" side was dry and thus won't have liquid run-off that's contaminated the underside of the board
It's not worth getting wrong. If you make a mistake and get food poisoning, or worse - give someone else food poisoning, you'll really wish you'd done your utmost to prevent cross-contamination.