When working with a rapier you use a very light touch, not just for safety reasons within the rules, but because that is entirely sufficient to kill someone and if you go any harder you are likely to get your blade bound up in their flesh.
This is true of a lot of narrowly pointed thrusting weapons, such as court swords: unless you are working to overcome metal (in which case for a court sword you are doing it wrong), there's more incentive to go light them to go heavy with the amount of force used. I've validated this with sides of beef, melons, etc.
It occurred to me, however, that this may not apply for a spear. Working with a straight-bladed spear (similar to a su yari, one without a crossguard in this case), for example: It's a wider blade and the shaft makes it easier to deliver harder strikes and have more leverage for removing the blade (and you frequently have two hands on it).
Assuming that I am not working to overcome hardened armor, should I be concerned about the blade getting stuck in an opponent and thus not use full controlled force on thrusts?