I've known of more than a couple of incidents involving inadvertent opening of spoilers that were not caught by the pilot and led to an accident or nearly so.

I was taught (by a German instructor) always to visually check spoilers when deploying them and again to check they were closed, something I have always done. I also only deploy spoilers when within safe distance of the field and almost never while flying cross-country. I remember a colleague who outlanded when he deployed his spoiler and the handle broke off, leaving them fully open!

Mike