Exactly the same as Andy in the above post. I think that most customers wouldn't really be too bothered, but why take the risk of giving them a less pleasant experience if it isn't necessary? One of the points in the guarantee I make to customers is that I will cause them the minimum amount of inconvenience possible, so if I needlessly drag a noisy bulky machine intothe middle of their house I feel I'm breaking that promise.
Terraced streets are a problem, so I sometimes just pull the machine inside the doorway to prevent any "Uncle Albert" insurance claims
This does present a bit of a problem in very narrow halls, as sometimes I need to get the rotary past the extraction machine. Shuffling one out and the other in does pee me off sometimes, but I don't do a lot of terraced houses anyway so just grin and bear it when the need arises.
I can only recall a handful of jobs where the 50ft of hose I normally carry won't stretch all the way and so I've needed to pull the machine inside.
Shaun makes a good point too, you're responsible for the indoor air quality of your customer's home. If I do have to pull my machine in further than the doorway so its rear-facing exhaust isn't blowing outside, I'll use my extension hose to vent the machine outside. This also has a bonus effect of cutting the noise down a hell of a lot!