Stores can get by without the use of greeters but one of the main reasons that stores such as Walmart usually ave door greeters is to catch shoplifters.
They have the store greeters at the door checking receipts for larger items to make sure you paid for the item.
But I do agree that store greeters are not really needed other than watching for shoplifters.
I always get annoyed by store greeters when they greet me coming into the store and going.
I also hate overly helpful employees who seem to ask me too many times if I'm finding everything I need as it makes me feel uncomfortable and annoys the heck out of me.
It also makes me forget sometimes what I came into the store for.
I wish employees would be able to just leave the customers alone until they need help with something.
Maybe ask the customer once if they are finding everything they need but don't ask again unless the customer comes to you.