King K. Rool's grabs have wide range and 3 active frames thanks to his nature as a super heavyweight character. As a result of this, these grabs are pivotal to his success. Unfortunately however, they're quite slow and the 4 frame lockout from grabs out of shieldstun significantly hurts standing grab as an out of shield option. Regardless, due to the reward King K. Rool can get off of grabs, they're crucial to his playstyle.
Standing grab has relatively good vertical range backed by K. Rool's stature, adding to its consistency, and even catching jumping opponents. Dashing into shield and then using standing grab (which isn't affected by the lockout due to absence of shieldstun) is a good bait option in neutral thanks to these qualities, as well as the fact it is less committal than dash grab. It's not uncommon to see K. Rool players abusing this for positioning purposes, as dash grab's sheer lunge distance can be problematic in some situations.
Dash grab has a significant lunge reminiscent of Captain Falcon's in Smash 4. This can be mixed up with initial dash's large dash grab window for mixups during approach, often alongside neutral attack for 50/50s. This makes King K. Rool's effective grab range quite wide as well, allowing grabs to be relatively easy to get against unprepared players. Dash grab is also very frequently used out of forward aerial pre-tumble as an early grab confirm. This usually leads into forward throw, and then a dash attack or Crownerang. It should be noted that dash attack cancelled dash grabs can boost the lunge distance even further, allowing K. Rool to potentially cover a Battlefield platform in distance[1]. However, the frame window for a good boost is high, in addition to the potential of using dash attack by accident, which makes it risky without practice.
K. Rool's pivot grab is a quick turnaround, extending exactly to his hand. Despite appearances, K. Rool's size makes the range deceptively large in practice. Due to how long the range of the pivot grab is, many K. Rool players make use of the C-Stick to do standing pivot grabs[2]. This is a fair alternative to dash attack cancelled dash grabs when running, though the execution barrier remains quite high. Given the active frames, useful hurtbox shift and coverage, this can also be used as a ledgetrapping tool against most grounded options. This is also a good option against opponents who abuse K. Rool's poor turnaround.
