Improve documentation of PROTO_NO_TLS
diff --git a/include/mbedtls/config.h b/include/mbedtls/config.h
index 1653f89..b701fbf 100644
--- a/include/mbedtls/config.h
+++ b/include/mbedtls/config.h
@@ -1521,7 +1521,8 @@
* \def MBEDTLS_SSL_PROTO_NO_TLS
*
* Disable support for SSL/TLS (all available versions) - this doesn't affect
- * support for DTLS which is controlled by #MBEDTLS_SSL_PROTO_DTLS.
+ * support for DTLS which is controlled by #MBEDTLS_SSL_PROTO_DTLS. This is
+ * useful to reduce code size in configurations where only DTLS is used.
*
* Disable this and enable MBEDTLS_SSL_PROTO_TLS1_2 to enable TLS 1.2;
* disable this and enable MBEDTLS_SSL_PROTO_TLS1_1 to enable TLS 1.1;