Well.. actually there is no difference. 절 is originally Korean word, and 사찰(寺刹) is Chinese-Korean word. I think we use 절 more when we just say 'temple'. Example: 이번 주 토요일에 절에 갈래? (Do you wanna go to temple this Saturday?) 오늘 절에 다녀왔어. (I went to temple today.) We don't really use the word '사찰', but every temple still has name in Chinese character, like 불국사(佛國寺), 조계사(曹溪寺), 범어사(梵魚寺). You can see the last character 사(寺) is same with 사 of 사찰.