Why is it that when building NGINX from source, all files in the /etc/nginx folder are duplicated??

Question

Nginx

When building from source, two files are created in the /etc/nginx folder, nginx.conf and nginx.conf.default, fastcgi.conf and fastcgi.conf.default, etc. Is it supposed to be like this or am I doing something wrong?
$ ./configure --prefix=/etc/nginx --sbin-path=/usr/sbin/nginx --modules-path=/usr/lib/nginx/modules --conf-path=/etc/nginx/nginx .conf --error-log-path=/var/log/nginx/error.log --http-log-path=/var/log/nginx/access.log --pid-path=/var/run/nginx .pid --lock-path=/var/run/nginx.lock --http-client-body-temp-path=/var/cache/nginx/client_temp --http-proxy-temp-path=/var/cache/nginx/proxy_temp --http-fastcgi-temp-path=/ var/cache/nginx/fastcgi_temp --user=nginx --group=nginx --without-select_module --without-poll_module --without-http_ssi_module --without-http_userid_module --without-http_auth_basic_module --without-http_autoindex_module --without -http_geo_module --without-http_map_module --without-http_split_clients_module --without-http_uwsgi_module --without-http_scgi_module --without-http_memcached_module --without-http_empty_gif_module --without-http_browser_module --without-http_upstream_hash_module --without-http_upstream_ip_hash_module --without -http_upstream_least_conn_module --without-http_upstream_keepalive_module --without-http_upstream_zone_module --with-http_ssl_module --with-http_gzip_static_module--with-http_stub_status_module --with-pcre=$HOHE/tmp/build/pcre-8.39 --with-zlib=$HOHE/tmp/build/zlib-1.2.8 --with-openssl=$HOHE/tmp/ build/openssl-1.1.0.tar.gz --with-cc-opt='-g -O2 -fstack-protector-strong -Wformat -Werror=format-security -Wp,-D_FORTIFY_SOURCE=2' --with- ld-opt='-Wl,-Bsymbolic-functions -Wl,-z,relro -Wl,--as-needed'