Many in society expect longer sentences for most offences,while the experts tell us that,generally speaking,custodial sentences,except in special circumstances,do more harm than good and that short sentences probably do less harm than long sentences.

　　要點：這是一個主從復合句。while在這里不是表示時間，意思是而。tell的直接賓語是兩個由that引導的從句：that custodial sentences do more harm than good和that short sentences probably do less harm than long sentences。except in special circumstances本事第一個that從句的狀語，但因為過長，所以插在主語和謂語之間。再者，這兩個從句中的比較結構是完全不同的：harm和good都是do的賓語，是在賓語中的比較，而than long sentences是兩個句子之間比較，long sentences后省略的謂語do(harm)。

　　譯文：社會上許多人期盼著對大多數罪行判處較長時間的刑期，不過，專家們告訴我們，一般的說，特殊情況外，判處監禁的弊大于利，短期監禁的危害性可能小于長期監禁。