Multiple instances or just one instance with everything feeding into it

Multiple instances or just one instance with everything feeding into it

HI,
Im setting up a new service desk for IT, and am looking for some advice.

setting this up so far has been fine, we have Incident and Service requests etc configured.

i have now been add to do the same for HR, Finance, Health and Safety, and Facilities.....

my question is, what should i do here, i had a look at setting up a new instance for each, but that comes at a cost, or could i bring everything under the one IT Service desk instance?

If anyone can offer any advice, that would be great.
how is yours set up? any tips or tricks?