first, ask as many questions as you have. We are here to help as much as we can and as far as I am concerned I love to help in any way I can
Pre-stain conditioner does occasionally help in many soft woods such as pine. The main effect it has on wood is to prep your wood for staining and providing a consistent base for your stain to adhere to and minimize blotching. Blotching is from areas in the wood where more resin is present than in other areas and can be frustrating to eliminate. Blotching can also arise because of density of the wood such as knots which take stain differently compared to clear areas.
With all of that said, does it really help ? My years of woodworking has shown me that a clear knot free board treated with a conditioner does help most of the time. If I am using a wood which has knots in it, I don't bother with it as it really does not help in my opinion.
I hope this is of some help and others will probably have a different take on this subject.
I have found it to be helpful. I make almost all of my projects from reclaimed wood or sawmill rough cut lumber. As Derek and Glen said it is most helpful with pine but I have used it on poplar as well. Even when knots are present it can be useful to get a cleaner stain on the board and to me makes the knot stand out more for a great looking finish. It all depends on what you would like the final outcome to be. I agree with the others, experiment with it and see what works for you.