Gripping, twisting and cutting when a full-size pair is not to hand: turning a stuck fitting, pulling a nail or a hook, twisting wire, and cutting wire with the built-in cutters. The plier head is what most plier-based multi-tools are built around, and it is the implement most owners use most.
Most plier-based tools combine a needle-nose section at the front for fine gripping, a broader gripping section behind it, and hardened wire cutters at the base of the jaws. Some add a crimping area. The jaws are only the front of the tool; the rest lives in the parts of a multi-tool.
Needle-nose is what makes them genuinely useful, because it reaches into places full-size pliers cannot.
Leverage. Multi-tool handles are short and often hollow, so sustained hard gripping is uncomfortable and less powerful than a dedicated pair. That is a physics limit rather than a quality problem.
Wire cutters on a multi-tool also dull faster than dedicated ones, because the jaws are smaller and the material is asked to do more.
Use the deepest part of the jaw for hard grips, not the tip, which is where jaws bend. For repeated hard work, use real pliers.