This is an interesting report (rather long, but the shorter key findings document is a good summary) about why SMEs file patents at the EPO.  

I have had discussions with SME clients about the reasons for them filing patents, and they have all mentioned the fact that it will help them in negotiations, possibly with regard to cross-licensing and co-operation with other entities, so the report agrees with my own experience.

The report also identifies some issues that SMEs have when looking to commercially exploit their inventions (for example lack of resources, skills or contacts) or in seeking collaborative exploitation (for example cost, the complexity of negotiations or identifying the right partners).

I think this one is worth a read if you are interested in the IP space and are in or working with SMEs.