Fo real?

Do you buy your shoes so as long as they are bigger than your feet it doesn't matter?

I realize this may sound like a strange question, but what is the exact effect of using finger inserts that are too large?

That is a strange question.  The answer, for me, is both comfort and aid in grip (these are one in the same for me).  I have some older balls with the grips worn a bit (too large) and they feel quite odd vs fresh grips.  They're still able to be used, simply not as comfortable.

Is the main reason comfort or does it aid in the grip?

Yes.

As long as your finger fits in the grip, why do we (or do we) care whether there is a lot of extra room or not?

Comfort and aid in grip.  More, to me, the former rather than the latter.

Thanks GT, that's basically what I'm thinking as well. Funny thing is this... After all the work I've done to get spans where I want them, for the last 3 weeks it's all gone away, and badly. Odd thing is, I accidentally ordered grips that were too large and started using them 3 weeks ago also since I didn't anticipate a difference. It's only 1/32 off in size from my norm. The most basic rule in troubleshooting is to always return to the last change, so I'm starting the hunt with grips, although I suspect, as Steven has mentioned in another post, I probably still don't have the span right. It was all great until I switched grips though... I admit it is odd.

I accidentally ordered grips that were too large and started using them 3 weeks ago also since I didn't anticipate a difference. It's only 1/32 off in size from my norm.

Another thing to note is using grips that are too big can shorten your span, Do to the thinner wall thickness of the insert. (Assuming the driller remembered to take the wall thickness into account for the cut to cut measurement when he mapped the span out on the ball originally.)

All good points, thanks.