Yale lock on the front door so that locks automatically when ever you close the door, I only use the mortice lock when I’m out of the house.
Back door, unless I’m in and out of the garden a fair bit I’ll keep it locked. Have also been known to lock it from the outside if I’m going to be in the shed with the door closed or using the turbo when I’m unlikely to see or hear anyone getting in.
My mum keeps her back door unlocked and mostly wide open during the Summer and she had someone walk into the house once, but her failing eyesight saved her. She thought the intruder was her grandson who lives with her. She said “Hello, I thought you were upstairs”. Which I guess made the intruder think there were more people in the house (there wasn’t, she was wrong on both counts) and he turned and scarpered.