The reception bonus options under receiving allow your league to specify different point values for the player catching the pass.
If you want to give more points for a tight end completing a reception, you would do that here. You could also give fewer points to a runningback making a catch.
It's possible that you have a player listed as RB/WR. They will never be able to get both reception bonuses.
First, it will depend on their official NFL primary position and not the fantasy slot you start them in.
If you have a player who is listed as RB/WR, their primary position is RB as it's the position that is listed first. If you started them in WR they would still get the RB reception bonus points because their primary position is RB.
If you start one of these players at a flex position, the player will be given the reception bonus based on his primary position.
*Note that all of these will stack with a standard reception if any points are given to the standard stat category (ie. PPR/Half-PPR)