What does Shakespeare's iambic pentameter do?

because he liked how it sounded in his plays

Iambic pentameter is a verse form, a rhythm of ten syllables where weak stresses alternate with strong ones, creating a sound like ta-DUM-ta-Dum-ta-DUM-ta-DUM-ta-DUM.Typical lines showing this rhythm...

In 1573, as part of his new religious reforms (because he had just become Pope in 1572) Pope Gregory XIII instituted the Catholic practice that all secular poetry was required to be written in iambic...

Much of it is. The Weird Sisters speak or chant in trochees.

all the times that he did not use iambic pentameter in his sonnets DUH