My concern is having a bunch of things randomly arrive the same month and then explain a $500 BLW charge on the "house" credit card...
More often than not, with these lengthy delays, my saved credit card has either been replaced for security reasons, or expired and replaced. The shop has to call for the new info to make the purchase, which might give me an out on the less desired stuff.
Sometimes, the shop just doesn't call, in case of hot sellers they can get rid of more quickly to someone with an updated card.
Also leaves me somewhat disgruntled. However, despite claims by others that stuff is impossible to find without a pre-reserved status, I have always found some of what I want, perhaps even saving myself from excess of the original order!
However, these kind of "sell to others" moments are greatly reduced since the 2000 and 2006 recessions. I recall pre-ordering from my LHS many Kato locos and they often claimed they were "shorted".