Two critical parts of any purchase agreement you negotiate are closing and possession dates. For the most part, if you’ve listed your house the buyer will expect to receive possession at closing. When that closing occurs will be based on a date that both parties agree to upfront. A seller may need to pack up and move or even find a house to move to. A buyer may need to get their loan application completely processed by their lender who will fund the purchase. Both sides may need to take into account vacations or move in/out dates for apartments or other rental properties.
An investor purchasing the house may agree to take possession of the house a week or two after closing with a security deposit held by the title company, possibly longer if some kind of rent-back situation needs to be arranged. In this scenario a seller gets the benefit of having most of the money from the sale to help with moving and relocation expenses, they also get to put the closing behind them which can be a stressful event to look forward to on the calendar.