The IBM PC and early successors came with an internal speaker that could play simple sounds. According to https://en.wikipedia.org/wiki/PC_speaker
However, because the method used to reproduce PCM was very sensitive to timing issues, these effects either caused noticeable sluggishness on slower PCs, or sometimes failed completely on faster PCs (that is, significantly faster than the program was originally developed for). Also, it was difficult for programs to do much else, even update the display, during the playing of such sounds.
That is the state of affairs I would expect if, like some early 8-bit computers, there was no sound chip and you had to bit-bang the speaker with the CPU at whatever frequency of sound you wanted.
However, according to https://en.wikipedia.org/wiki/Intel_8253 the 8253 timer chip was connected to the speaker and capable of generating a square wave, which suggests the CPU should only need to intervene when the volume or pitch needs to be changed, which would normally happen no more than a few times per second.
What am I missing?