I sometimes buy my kids diapers on Amazon when I don't feel like going to the store or when I can find some deals.
If I need the diapers right away then I just go to the store.
Sometimes the store is out of stock of the diapers I plan to buy which are pampers baby dry and pampers swaddlers so If I check online at Walmart.com to see if Walmart has any of the diapers in stock at that store and they don't have them in stock at that time then I will order the diapers and have them shipped.
Sometimes Walmart.com will have them in stock where I can buy them from Walmart online and have them shipped.
I prefer ordering stuff that I can order and have it shipped to my door instead of having to go into the store.
However if I'm already gonna be at the store such as for Grocery Shopping and I need to get some diapers and they have the diapers in stock then I will go ahead and buy a box or two of the diapers while I'm there.