The use of the L1 in the L2 classroom

I think most teachers agree with the idea that the L2 should be used as much as possible in the L2 classroom. Most students probably agree too, but of course there are always exceptions.
I too think it is important to use the L2 as much as possible, but there are situations when I prefer using the L1 which is Swedish in my case. When talking about grammar I tend to use mainly Swedish, but I think that is about the only situation when I make an active choice between Swedish and English. In other situations I start off in English and finish in Swedish, for example when giving instructions or talking about homework when I notice that the students don't seem to understand what I am on about.
However, yesterday I noticed a situation which has been discussed in the course literature and that is showing that you have understood a text. My A-course students have watched a film called Stone Cold and it was divided into three parts. Before we watched the last part I asked them to just retell what happened in the previous episode. They did this in Swedish and retold the whole episode and thereby showing that they had understood what happened. Had they done this in English they wouldn't have retold half as many details. This is mainly due to lack of vocabulary and not knowing how to express what they want to say. But it got me thinking - should we once in a while let our students talk about or retell what they have read in their L1 instead of their L2 to get at better picture of their interpretation of the text? If they only ever talk about texts they have read in their L2 we might actually miss out on their thoughts and ideas just because they do not have the words. Then on the other hand you have the fact of practising using the L2 in different situations.
It is a totatlly different story with my C-students because many of them are very fluent in English so for them it is not that difficult to express their thoughts and ideas.
To sum up, what I mean is that sometimes we might let our students use their L1 to show their actual understainding of a text. What do you think?

//Linda