Does anyone know what the uses of these parts are?
1-Post Standoff Retainer with Bearing Flat: when would you have a shaft next to a standoff?
shaft Collar Retainer with Bearing Flat: how do you tighten or loose the shaft collar if it is inside a holder?
Here goes the pictures so you don’t have to look them up like I did. 
For the first photo, I have actually never seen on anybody’s robot or in our workroom, so I don’t have any experience with them. It looks like a shaft collar is inside of the bearing which might actually be a good idea if it is executed properly. You could use it to leave space for things on the shaft like gears or wheels for some reason if you have 2 wheels on 1 shaft??
For the second photo I have seen them in the workroom, however, I have never used them because I thought they would be less secure than just regular bearings because there is only 1 hole for a screw and the other is just a square going into a hole.
All in all, I think the 1st photo is actually usable the other seems just like a unsafe bearing. Correct me if I’mwrong…
Also the post standoff retainer is the bottom one and theshaft collar retainer is the top
As a teacher, I can tell you that both these parts are standard in VEX EXP kits. The hexnuts in those kits are smaller (same size as a standoff) so the standoff retainer actually can be used like a V5 1 post hexnut retainer. As for the shaft collar retainer, EXP kits have only the rubber ones, so it helps those stay on better with the retainer (although you can’t use the retainer and put it after a wheel, for example)