I use foliar feeding to build-up calcium, magnesium and trace element levels, besides supplementing base nutes. I generally add CALiMAGic and Earth Juice Microblast, plus a dose of N, whether as a high N cal-mag, such as Adv. Nutrient's Sensi Cal Mag Xtra (4-0-0) or the N part of Adv. Nutrient's 2 part pH Perfect base nutes, doing this using Transfer/Optic Foliar to feed through top surface of the leaves. Contrary to all recommendations I've seem, I just use everything at the same level I use in regular feeds; and I've seen no downsides, such as excesses, from this.
I may do this 2x/week from sprouting to early bloom. If a plant is more advanced in bloom and looks needy, I sometimes will let the aerosol droplets fall onto the plant. That way any wetted surfaces will be well exposed to air (and with my tent relative humidity at best usually getting up to 40%, I don't worry about this causing mildew problems).
Definitely check out Transfer/Optic Foliar and its feedback here on AFN. I think it is more effective than traditional bottom-of-leaves foliar feeding. You can even see it working - sprayed fluid disappearing into the leaves way faster than it could ever dry from air exposure.