Hi Simon, how about a little bit more info, brand, model...
LXI is standard to communicate with instruments via Ethernet. Usually you just send normal SCPI commands and instrument obeys... or not :-)
You can use Python with libraries, Scilab, Octave.... Or Labview, MAthlab.... Or software from manufacturer if there is one.
Usually you use to automate some measurement procedure, testing process or something... Or calibrate.
Generally for repetitive and boring stuff while being sure it was done exactly as it should be.
So that's general overview. For more details, provide more details..
EDIT:
I see it is TTi, what model? TTi is good brand, they have good manuals with full SCPI command set to use...
Regards,
Sinisa