If the administrator used a subnet for the allow-transfer option for testing purposes or as a workaround solution or set it to any, everyone would query the entire zone file at the DNS server. In addition, other zones can be queried, which may even show internal IP addresses and hostnames.
DIG - AXFR Zone Transfer - Internal
z3tssu@htb[/htb]$ dig axfr internal.inlanefreight.htb @10.129.14.128
; <<>> DiG 9.16.1-Ubuntu <<>> axfr internal.inlanefreight.htb @10.129.14.128
;; global options: +cmd
internal.inlanefreight.htb. 604800 IN SOA inlanefreight.htb. root.inlanefreight.htb. 2 604800 86400 2419200 604800
internal.inlanefreight.htb. 604800 IN TXT "MS=ms97310371"
internal.inlanefreight.htb. 604800 IN TXT "atlassian-domain-verification=t1rKCy68JFszSdCKVpw64A1QksWdXuYFUeSXKU"
internal.inlanefreight.htb. 604800 IN TXT "v=spf1 include:mailgun.org include:_spf.google.com include:spf.protection.outlook.com include:_spf.atlassian.net ip4:10.129.124.8 ip4:10.129.127.2 ip4:10.129.42.106 ~all"
internal.inlanefreight.htb. 604800 IN NS ns.inlanefreight.htb.
dc1.internal.inlanefreight.htb. 604800 IN A 10.129.34.16
dc2.internal.inlanefreight.htb. 604800 IN A 10.129.34.11
mail1.internal.inlanefreight.htb. 604800 IN A 10.129.18.200
ns.internal.inlanefreight.htb. 604800 IN A 10.129.34.136
vpn.internal.inlanefreight.htb. 604800 IN A 10.129.1.6
ws1.internal.inlanefreight.htb. 604800 IN A 10.129.1.34
ws2.internal.inlanefreight.htb. 604800 IN A 10.129.1.35
wsus.internal.inlanefreight.htb. 604800 IN A 10.129.18.2
internal.inlanefreight.htb. 604800 IN SOA inlanefreight.htb. root.inlanefreight.htb. 2 604800 86400 2419200 604800
;; Query time: 0 msec
;; SERVER: 10.129.14.128#53(10.129.14.128)
;; WHEN: So Sep 19 18:53:11 CEST 2021
;; XFR size: 15 records (messages 1, bytes 664)