It's cheap
£100-£180/week for a private room is genuinely cheap. If you don't mind a stranger's kitchen and bathroom, it's hard to beat on price alone.
The trade-off is friction
You're a guest in someone else's home. Their rules, their schedule, their TV preferences. Some homeowners are great about it. Some forget. For a 6-week stay it can get exhausting.
Crews of 2+ tip the scales
Solo contractors sometimes prefer lodgings on price. The moment you've got a colleague with you, the per-person price gap between lodgings and a TNS whole-house shrinks dramatically — and you'd rather share a house with your colleague than with a stranger.