There are instances where clipping is acceptable, though only if it is proc related or a cool down skill with an extra buff. For example, with summoner using Tri-disaster when it pops on dreadwyrm trance for its ruination buff and to keep dots up while you ruin spam, even if dots are still up. Or with black mage, you typically want to use thunder whenever it procs for the extra damage even if that dot is up. Otherwise you only want to reapply a dot only if it's within its last few seconds to keep uptime going.