I operate in a busy Class D environment requesting squawk regularly, and as such was taught as a student to always switch on the transponder. Even if away from my home airspace in the open FIR I have the transponder switched on. Fisbangwallop and his colleagues usually ask us to squawk 7401 anyway if we are using 119.87.
At least if you are being painted by a radar unit you are easily identified if you have a squawk. Useful if things go mammaries skyward for whatever reason...
Don't understand people who fly around with the transponder switched off... if its there, use it.
Smithy