Value refers to the number of turns remaining that a form can stay out before having to be absorbed. If a form has not been absorbed prior to running out of fuel, it remains capable of moving and fighting, but it will lose some Health. For each turn that it is out and unfueled, it will lose 1/5 of the normal total Health for that Form Type (ie, a Colossa would lose 300/5 = 60 Health/turn). If a Form's Health drops below 1 because of this, it dies. When summoning a form, you fuel the form for a number of turns between 1 and the form's maximum fuel.