Vては is used as a problematic conditional with expressions that indicated a negative evaluation or an undesirable outcome, and is often used when recommending that outcome be avoided by avoiding that particular behavior.
僕はアルバイトしては レコードばかり買っていたから、一日半働けばLP一枚買えるな、と思って働いていた - I went to work thinking that if I worked a day and a half, I could buy one LP if I had a part-time job because I would only buy records. (taking a job just to pay for silly records)
そんな大きな声を出しては魚が逃げてしまう。- Such a loud voice will scare the fish away. (You should be quiet)
コーチがそんなに厳しくては、誰もついてきません。If the coach was that strict no one would go along with him. (the coach should be less strict)
