[CrimpJiggler]

In splitless mode the whole sample is injected into the mobile phase whereas in splitless mode, most of the sample is vented out before it reaches the mobile phase. Why would one opt for split mode over splitless mode?

[orgopete]

With high sensitivity, you don't need a lot of sample to get a response and to maintain response linearity.  If you have a capillary column, a small and narrow sample injection will give sharp peaks in the effluent. Practically speaking, this is more easily done by splitting the sample.