Yeah, it's about setting and managing expectations. Small favours can help build relationships, discounts can help close a deal, and so on. Less relevant for larger clients, but may be necessary when working with smaller clients.

Writing it down can be the difference between the client thinking "I understand what you did there is a one-off favour and I appreciate it", versus the client taking it for granted as something normal and always expecting it in the future at no cost / discounted cost.