Mixed, but sometimes there's trunking on walls yes. I have a little bit of that (for something disused actually, plan to remove, I've not long moved in) but it's mostly under floorboards. (There are also would-be exposed pipes in the kitchen, hidden behind counters, I believe - but they probably would have done that anywhere, that's a relatively modern extension.)

Insulation is a more complicated topic - if you're going to do it you need to do it differently, since modern new-builds and modern insulation is designed around making everything air & water tight, which will make an old house very damp and rotten (which will lead to woodworm/boring beetle) - the structure needs to 'breath'.