Explanation
According to the web search results, Auto TX Power control is a feature that allows the AP to automatically adjust its transmission power based on the RF environment. The goal is to minimize interference and optimize coverage cells for roaming. When the AP detects any other wireless signal stronger than -70 dBm, it means that there is a potential source of interference nearby, so it will reduce its transmission power until it reaches the minimum configured TX power limit. This will reduce the interference and improve coexistence with other devices. When the AP detects any interference from a trusted neighboring AP stronger than -70 dBm, it means that there is a high density of APs in the area, so it will also reduce its transmission power until it reaches the minimum configured TX power limit. This will balance the load and avoid overlapping coverage areas.
References: AP Transmit Power and Enable Power Reduction with Auto TX, Transmit Power and Antenna Configuration, Meraki Auto RF: Wi-Fi Channel and Power Management