I tend to buy a bottle when I'm almost out. But now when I find it I usually buy two bottles at a time.
Regardless of prepping mentality or the circumstances, I think it is wise to buy a few more than we need. It saves time and frustration. If you have a pantry or enough space , it is wise to have your own "store" at home, especially for non perishable items like soap ..etc.
Sometimes, you are not in the mood to go out, or the roads are congested for a reason or another, or the weather... etc. There are a million reasons that we should store a few extra of everything. Find a balanced level that is suitable for your lifestyle and size of your family, and I think no one will regret having a few things stashed in the pantry.
During the pandemic lockdown, two of the kitchen appliances broke down. When things eased a bit, I bought TWO of each.