I was discussing preparation versus non-preparation with some other SMTs a few weeks ago at a conference, the thoughts were very interesting.
Basically there seemed to be two schools of thought with teachers - those that find/found SATs useful and those who do not. There's very little ground in between. The teachers that detest SATs generally do so because they see it as a big distraction to their teaching strategy. They dismiss it as being 'useless' to the school and child and that it will only result in the child becoming 'stressed/anxious' and likewise the teacher. They generally don't recommend children practice or prepare for them at home, indeed they wish everyone would just forget about them. I can sympathise with this, especially when you consider that they may see it as an invasion into their classroom. The 'no point' argument though, as an SMT, is silly.
The SMT folk that do like SATs though see things slightly differently. Whilst it is a distraction to the NC, they see the exam procedure as being good practice and preparation for the future. They also generally agreed that if they do stream the children into KS3, then the basis for this will be KS2 results. They generally wanted the parents to be actively involved in preparing the children for their SATs tests.
Both the pro-SATs and no-SATs SMTs agreed that when a child achieves a good SAT level, they carry this boost into the classroom. Both also agreed that the parents can make the children overly anxious about performance in their SATs, however it's difficult to really say whether this is significant since it's only the anxious parents that they tend to have contact with!
Personally, I always liked KS2/KS3 SATs. What we have now achieves the same thing but takes more time and is ironically more of an inconvenience. Besides, KS3 kids could really do with more tests before they hit GCSEs.