Most insurance companies specify window locks on their questionnaire, and although that doesn't answer your question it gives an illusion of security. Breaking 2g or 3G glass is not what most opportunist thieves do so I guess we're left with preventing egress, possibly kids? or my dog, who can open doors.
I once had an outbuilding broken into, it had recycled bog standard wooden windows 2G, outward opening casements with locking handles. They had forced a screwdriver into the rebate just under the handle and clouted it with a hammer and the the cheap handle just gave way and the window prised open.

I also worry about egress in the event of smoke, fire or emergency — the last thing you would want to do would be to have to find a key

I think the point is that a burglar's first concern after gaining entry is to secure a quick means of retreat in case of surprise.

I agree

When i was first burgled, ( early 90’s) , the miscreant had entered through a rear window, then internally locked the front door, the idea being that if the homeowner returned unexpectedly the rattling of the key in the lock would alert the thief who’d then have time to escape out the back, this depriving the homeowner the opportunity of doing the ne’er do well any well deserved harm.
On that occasion they’d first tried kicking the back door in, it had a nice array of shoeprints, then levered open a casement and the stay just broke.
2nd time ( almost exactly a year later) they came in the same way ( this time the screws ripped out of the timber frame, went for upvc after that) set the alarm off that had been installed , stacked my stereo , tv and other stuff outside the front door and were caught by police ,who’d attended having been called by a neighbour, when he returned at that point in a car he’d nicked. Total scrote junkie , got a total of 3 months for my place, another forced entry where he beat the occupier unconcious and the car he’d nicked.
Fortunately karma lent a hand and a couple of years later he OD’d.

My front door is English style inwards opening. My back doors are the same design but outward opening. Historically I think it used to be that outward opening meant hinges on the outside and hence easy to take the door off, but I don't think it makes much difference these days with hinge bolts and multi-point hook locks.

I think I've heard it mentioned but I don't remember when. Basically, no locks on escape windows. It's all a compromise (bodge?) between 'security' and 'safety'.

The Secured by Design guides - https://www.securedbydesign.com/guidance/design-guides - include advice on where there should be locks, which seems sensible to me:

Short version: All easily accessible windows should incorporate key lockable hardware unless designated as emergency egress routes within the Building Regulations. Where 'easily accessible' means:
- A window or doorset, any part of which is within 2 metres vertically of an accessible level surface such as a ground or basement level, or an access balcony, or
- A window within 2 metres vertically of a flat roof or sloping roof (with a pitch of less than 30°) that is within 3.5 metres of ground level.

The locks on the windows in this house are the weirdest (still in from when we bought it).
They have a thumb button - the sort you would expect to press in order to be able to turn the handle, which seems to be how a lot of them work that you see.
But on these ones, when you press the button, it locks it. Then you need the key to unlock it to get the thumb button to pop out again. To open it you have to turn the handle WITHOUT pressing the thumb button.
Counter-intuitive, and unsafe for upstairs windows in my opinion.

Posted By: Dominic CooneyThey have a thumb button - the sort you would expect to press in order to be able to turn the handle, which seems to be how a lot of them work that you see.
But on these ones, when you press the button, it locks it. Then you need the key to unlock it to get the thumb button to pop out again. To open it you have to turn the handle WITHOUT pressing the thumb button.

The ones on our windows work like that too. As you say, very counter-intuitive.