This is a complicated subject, especially when you consider trimming and pointing.
The overall answer to the question: "how much do these operations (pointing and trimming) help?" can be answered by: "It depends on how bad (large and inconsistent) the bullet tips are to begin with".
For bullets that have small and consistent meplat's out of the box, it can be a waste of time to trim and/or point.
But if you have bullets with very large and inconsistent tips, you can improve the bullets a lot with these operations. Any by 'a lot', I mean something that will be visible in 1000 yard groups, but not necessarily to those shooting steel at various ranges from improvised positions.
Now, to get into the details...
To start with, consider the fundamental differences between trimming and pointing.
Trimming is purely a uniforming operation. The trimmers index off the bullet ogive, so they always cut the tip to the same diameter. This isn't necessarily cutting the bullets to a uniform OAL. The important thing is you're getting tips which are all the same size. Done correctly (meaning you set the trimmer to trim the correct amount), trimming will uniform BC to the lowest BC bullet in the box. In other words, the bullet with the largest tip in the box is the bullet that you want the trimmer to barely touch, and all the other bullet tips will be trimmed to this size. So with trimming you're uniforming the bullets, but slightly lowering the overall average BC.
Pointing is different in the sense that the operation is indexed from the base of the bullet (the bullet is pushed into the pointing die from it's base). Because of this, and the fact that not all bullets are the same OAL (even after trimming), bullet pointing doesn't guarantee uniformity, but it does have a uniforming effect because it's taking bullet tips that may start out very different, and making them 'less different'. The main advantage of pointing is an increase in average BC.
Trimming before and/or after pointing doesn't guarantee total uniformity because the trimmer is trimming the nose to length and leaving OAL variation, and the pointing operation is based on OAL, so you'll still have some bullets pointed more than others. (the longer bullets will be pushed further into the pointing die).
If you really want the 'best' possible procedure for uniforming and increasing BC, this is what I recommend.
First, trim all bullets.
Next, sort bullets into batches of OAL which vary no more than +/- 0.001". Depending on the uniformity of the bullets, this may be 2 batches or it may be 10.
Now, with the bullets trimmed and sorted into batches of common length, set your pointing die to point the first batch. When the first batch is finished, make an adjustment to the pointing die to accommodate the length of the next batch of bullets. If you don't, you'll be pointing more or less due to the difference in bullet OAL.
I don't see a benefit in trimming again after pointing.
In fact, I think you can arrive at the 90% solution by skipping the trimming step, and just sorting bullets on OAL before pointing.
Having said all that, for my personal use in competition, I just point my bullets straight out of the box. Granted, these are Berger Bullets which tend to come 'out of the box' in pretty good shape and don't need much work. I've never trimmed bullets except for test the effect on BC.
Many times shooters get lost in the weeds of how much this or that helps. Remember the overall universal answer: it depends. One shooter may demonstrate a great benefit to trimming and pointing 'brand x' bullets that he shoots in a certain application. It's unwise (but very common) for other shooters using different bullets in a different application to jump to the conclusion that they need to do the same thing that helped that guy. When considering pros and cons, consider the details of the application before blindly following what other successful shooters are doing.
Take care,
-Bryan
