to maybe clear things up a little bit, think of the splitter as like a big Y splitter. it's useful for when you want to split the dmx signal wire to go in 2 or more directions.
an example, but not limited to...
say your dmx signal just left the house, you could place a splitter right outside the house, so you can run a line to the left side of the yard, then another to the right side of the yard, plus have an extra line to go to the roof.
if you have 3 items in a small area, you don't have to split up the signal as most dmx equipment can be daisy chained. but it's really up to personal preference.