〜一方（で）

便利になる一方で、失われたものもあります。

Benri ni naru ippō de, ushinawareta mono mo arimasu.

As it grew convenient, something was also lost.

一方で sets two things side by side; they need not belong to one thing

都市部が過密になる一方で、地方は過疎化しています。

Toshibu ga kamitsu ni naru ippō de, chihō wa kasoka shite imasu.

Cities crowd while the regions empty out.

Commentary uses it to lay out two faces of a society

反面 は同じ物事の両面に限られます。

Hanmen wa onaji monogoto no ryōmen ni kagiraremasu.

反面 is limited to two sides of the same thing.

That is the practical test between the two