I'd certainly be inclined to maintain tyre pressures at a reasonable level - not letting them drop below ~50psi if possible.
If you allow the tyres to deflate completely with the weight of the bike on them (I'm assuming you're not suspending it) you could find them permanently deformed next Spring. You might also find that a tube is trapped so that when you pump it up you get an almighty blowout. Give brake pivots and derailleurs a dose of WD40, TF2, GT85 or similar to dispel moisture, grease all exposed cables. That's probably about it.
Prseumably you have a Winter hack, and aren't giving up riding for the next 4-5 months?