Losing a half gallon during racking is not the same as leaving out a half gallon of water when you start out. The wine you lose during racking has no affect other than to reduce the volume of wine you end up with. Leaving water out when you first mix it with the juice alters the balance of the whole batch - higher SG; change in potential ABV, possible residual sweetness, etc.
Yes, I'm aware of all that. Yet, it seems to be a very common practice, which is why I asked about it in relation the type of wine I'm making. As I said, losing a small amount is not my concern--the fact that I have only a 5-gal carboy for secondary is.
jpwatkins9, thanks for the up vote on the Cote des Blancs. That is what I ended up ordering, since Amazon had for next day delivery, and I read comments that it does well with cider too, which I like almost as much as wine, so the extra packets are more likely to get used.