一方で: comparing two coexisting aspects
Present advantages and disadvantages or different groups' activities side by side. Avoid reading causation or a time sequence, and distinguish 一方だ for a one-directional trend.
Two aspects of the same subject
この町は静かな一方で、買い物には不便です。 means that the town is quiet but inconvenient for shopping. Quietness and inconvenience coexist as different dimensions of evaluation.
The sentence alone does not establish that quietness necessarily causes inconvenience. 一方で presents the two aspects; a causal relationship needs other evidence.
Contrasting different subjects too
兄は外で働く一方で、弟は家で仕事をしています。 contrasts an older brother working outside the home with a younger brother working at home. The subjects can differ; the same person need not perform both actions.
This comparison does not require both people's working hours to match down to the second. Distinguish presenting activities alongside each other from asserting simultaneous activity at every instant.
Connections and comparison with 一方だ
Verbs and i-adjectives connect in plain forms; na-adjectives use forms such as 便利な一方で. 彼は教師である一方で、作家でもあります。 presents the two roles of teacher and writer together.
物価が上がる一方です。 describes prices continuing to rise. 物価が上がる一方で、収入は増えません。 contrasts rising prices with income that does not increase, so check what follows で.
Quick check: Does 便利な一方で、費用がかかります。 mean something was convenient at first but later stopped being convenient?
Show the answer and why
No. It presents convenience and cost as two aspects together. It does not express one state replacing another over time.