Guide coat is just that... A guide. I use a lot of SEM products and usually use the trim black because I have it on the shelf. The idea is that you mist on a guide coat that you will sand off.
Everyone has their own way of doing body work that works for them. I do a number of high end restoration a year with my business and I guide coat every time I block primer. It certainly doesn't hurt and if you can block straight each time you prime, so why wouldn't you use that guide coat every time?
My .02 worth!
