Divided lites used to be the only way to make a large window. Large panes of glass were impossible or very expensive.

That's not true any more, but the "old style" is aesthetically pleasing to some, and sometimes even required by law for old houses.

Today, True divided lites are more expensive -- more material, more handling, more assembly.

And simulated divided lites are a cheap way to pretend to be expensive, or historically correct.

I always rip 'em out, personally.