TL;DR: what normally crew-served or heavy weapons could be used as infantry weapons by something larger and/or stronger than a human?
Let's take the M2 Browning, or, rather the .50 Browning round it fires. The amount of armor steel each round can penetrate is impressive - it can blow through brick/cinderblock walls and cut down trees with ease. Its lowered rate of fire in comparison to actual handheld infantry weapons is negated by the fact that the round it fires is big, and since the round is so massive in comparison to smaller ones, its energy falls off less quickly than them. Moreover, its high ballistic coefficient (it slices through the air more easily) means that it doesn't get blown off course as much as smaller rounds. In short, it's a very powerful weapon.
The problem is its weight.
A cursory Google search reveals that its weight, even without ammunition or its tripod/traverse-and-elevation mechanism, is 36 kilograms. On average, its ammunition is about 100 grams per round; if this hypothetical M2HB-wielding soldier wants to carry 100 shots, they're going to have to cart around about 10 kilos of ammunition, as opposed to ~1.23 kilos for a soldier armed with something that fires 5.56x45mm NATO who wants to carry the same number of rounds.
Additionally, there's the recoil. The Wikipedia entry for the .50 BMG cartridge states that its bullet has a mass of between 42 and 52 grams, and a muzzle velocity of between 860 and 928 m/s. Even assuming that the M2HB fires rounds that weigh 42 grams at 860 m/s, and not more, which I personally find somewhat unlikely, considering its impressive barrel length, the M2HB's Wikipedia entry, and the fact that those velocity and mass figures are not from the same round (they're the smallest ones I could find for a .50 Browning round), this recoil calculator gives me a recoil of 5.87 feet per second. If I swap in the largest velocity/mass figures I can find for a .50 BMG round, I get a rather-chunkier 6.96 feet per second. In comparison, even the largest figures I can find for a 5.56x45mm NATO round fired out of an M-16 gets me a 2.98 foot-per-second recoil.
The M2 is also just used for the purposes of reference; think about everything, from anti-tank missile launchers and recoilless rifles to miniguns and flamethrowers that don't work as human infantry weapons but work for larger entities.
If you need a specific entity for the purposes of answering this, imagine something that's 9 feet tall and 240 kg/529 lb, and comparable to an Olympic athlete in terms of physical capabilities related to weightlifting, physical endurance, or stamina. It can be mechanical or biological - it's just being used as a reference for the purposes of measuring how its increased size/strength relative to a human effects its ability to carry big guns.