An army marches on it’s stomach and it’s not very useful if your soldiers are passing out from dehydration. Pioneers were the auxiliary troops and camp followers, providing rudimentary first aid (bandaging was about the limit) and making sure that the soldiers had access to
Mattrosses had a specific role in holding onto the musketeers’ lit match, especially when they were going in to close quarters. Nobody wants a stray ember reaching a black powder store!
Pioneers today are the first stop in making sure that the on-field members are healthy and safe.