Their drop table is poor overall,with RuneScape gold most of their loot being either low-value or rare drops like the Ensouled Head or Smoldering Stone. You will almost always lose money on this task,so unless you need the occasional clue or just want an easy task to kill time,these creatures are best blocked.
Cave Krakens
Cave Krakens,much like Hellhounds,have a high Slayer task weight,which means you'll be assigned these more often than you'd like. These monsters are particularly slow to kill since you can only use magic-based attacks,like a Trident of the Swamp,and you can't utilize melee or ranged combat.
This results in very low XP per hour. The Kraken's drop table also doesn't offer much in the way of profit,making this a task that's better blocked if you value efficiency. Their high task weight makes them a prime candidate for your Block List.
Black Dragons
Black Dragons are a bit of a hassle to deal with,mainly due to their high Hitpoints and the need to bring anti-dragonfire protection (either a shield or an antifire potion). If you want to kill them efficiently,you'll need a Dragon Hunter Lance,which is an expensive weapon,and its use is generally limited to Slayer. Duradel typically assigns only 10-20 Black Dragons per task,but this isn't ideal for XP gains. We're looking for tasks where we can kill larger numbers of monsters in the same location for cheap Runescape gold maximum experience,so Black Dragons don't fit the bill.
