I use it as a foliar feed when the seedlings are young...probably once a week/two weeks, but when I apply it, I apply it pretty heavy...I don't wash it off...just let it dry...the plants respond to it pretty quick...within a day you can see changes.....the biggest thing you are doing is making sure the plants have enough magnesium...magnesium is water soluable and will be washed away with each watering...when the plants are transplanted to 5 gallon containers, they get about a big tablespoon of epsom salt on the soil surface as a "side dressing"...then each time you water, the salt is disolved and becomes available for the roots to take some up...I side dress with epsom salt and a standard 10-10-10 peletized fertilize once a month during the grow season (May-Mid-August), then Mid August, I switch to a 7-14-7 or something like that....
I hope you understand that each person has to do it the way that works for them...with your grow season shorter than mine is, the way I do it may not work for you...I have adapted to the seasonal changes down here...I lose July and August production because of the heat, but the plants flourish in the heat and become very big...when the weather cools in September, they have 3 full months of production...
As far as it helping goes, I really don't remember all the reasons I do it, but it is mostly because Grandma Mattie did it and she grew gorgeous tomatos and peppers and she learned from her grandma......so it is just my standard routine for growing the plants...and has been for many years...I sure don't think it hurts and epsom salt is cheap...
sorry to ramble...just thinkin' out loud...