Gist

Yes, especially when the knee stays straight enough to keep gastrocnemius long while the ankle moves through plantar flexion.

Yes. The soleus is a powerful plantar flexor and is trained by calf raises, including bent-knee variations in which gastrocnemius contribution is reduced.

Yes. Calf raises directly load plantar flexion and can build both major calf muscles when the variation, range and weekly work are appropriate.

They build a specific portion of the legs: mainly the hamstrings. They do not provide balanced development for the quads, glutes and calf muscles on their own.

No. Leg curls train knee flexion, while the quadriceps perform the opposite action of knee extension.

They may train gastrocnemius slightly because it crosses the knee and assists knee flexion, but leg curls are not a reliable primary calf-building exercise.

Not substantially. Leg curls challenge knee flexion, whereas the glutes are built most directly with loaded hip extension or hip abduction work.

Yes. Leg curls directly load knee flexion and can increase hamstring size, particularly when the movement is trained consistently through a controlled range.

They can strengthen the grip and provide some forearm stimulus, especially when heavy sets are held without straps. They are not the most complete forearm exercise.