Wow that sounds exciting doesn't it! Not! 1/4 inch seams! The reality is though that this is one of the feet that I use the most.
This foot is brilliant because what it does is leave you with a perfectly even 1/4" inch seam/hem. I love to use it when hemming garments and it does leave a much more professional look to all items if you have a perfectly straight line! Brilliant for topstitching on items too.
The foot had a black metal guide on it's right hand side and you simply place the edge of your fabric against this edge and sew! Simple as but oh so effective!