Some touch spells, such as Chill Touch, give you multiple charges to attack with, but these charges can be discharged even on accident or by the action of someone other than the caster, but what happens if the contact is continuous such as when grabbling or when holding on to someone, then how quickly can the spell charges discharge?
Such spells can discharge without an attack so it can't be by attacks made.
If we look at the maximum number of possible touches without continuous contact, you get around a dozen maximum (the number of touch attacks the caster makes, touches from attacks of opportunity which would be one or possibly two, and then the number of touches from the target touching the caster from their attacks. So, with 4-6 attacks per round at high level by the caster and target, plus one aoo from the target and you get 9-13 touches.)
Of course, spells expecting multiple touches is 6 per round, but that assumes the caster is going from one person to the next multiple times which is about once per second, and also assumes all the touches occur on the caster's turn, both limits do not apply to chill touch (or similar) in a grapple.