Second, it makes you think about the forces on your gear from different angles. When you top-step, will that nut get pulled out? (RG knows what I'm talking about!) Can that tricam take a force from the side? GO
I believe you can achieve similar results in sling testing in "ground school".
Hmm, I suppose you could, if you rigged up an aider and climbed up on the piece. But then you're risking a more nasty groundfall. All my groundschool consisted of simply bouncing straight down on a piece. When you top-step, you're putting a lot of outward force on the piece. Something that certainly can also happen in real lead falls (causing gear to zipper).
Once again a bit off the original thread, and with the disclaimer that I am a self-taught and not terribly skillful aider, do you guys place gear differently aiding then free climbing? I find myself often reaching high and making placements that are difficult to adequately, or impossible to, visually inspect. Sometimes doing it by entirely by feel. I rely on bounce testing to ensure the "goodness" of the placement before fully committing to the aider attached to the piece. My motivation is, I guess in hind sight, is to maximize my progress up the pitch. This is very different from when I free climb. Then I very consciously attempt to place gear at chest or waist level to ensure a very good look at the placement. For point of reference, since both of you lead at significantly higher level than me, I am currently leading 5.8's at the Gunks and looking to start rountinely doing 5.9's this season.
Personally, I don't place gear very differently. I sometimes place gear super-high when aiding, but only when it's the only option. Whether I'm aid or free climbing, I like to be able to see what the placement looks like. When aiding, and will often top-step (or at least one from the top) even when it's very strenous, to get at least one really good look at the piece, before climbing back down the aiders and bouncing it. Adjustable daisies would probably make this much easier, but I still just use a fifi and a standard daisy.
Also, when free climbing, I usually place the piece above my head, because A - I'm a wimp, and like having a TR whenever possible, and B - it means I can go further before feeling like I need to place the next piece.
Honestly, if you're just placing gear by feel when aiding, I don't think this has as much application to your ability to place while free climbing (except when you're forced to place blind while free climbing).