Peer Registration

[MMliam]

ESPNow is a communications protocol developed by Espressif to address long latency connection time of wifi.
I'm using ESP8266's & ESP32's with microPython; both using ESPNow communications. Using an ESP8266 as a sender doesn't require the ESPNow peer registration, however the ESP32 microPython does require an ESPNow sender to register peers.

What is the rational for "registration"?
As understood there's a limit of 10 encrypted devices, or 20 unencrypted devices; is this due to a fixed registration data array size?
If there is only a single receiver, it appears that any number of senders (ESP8266, or ESP32) can be used; is this true?

MM