I don't have one, TBH if there are things untoward going on around my door when I'm not there, I'd rather not know, although I appreciate it might be useful for deliveries etc.
However, a friend uses hers to monitor her family's coming and goings, e.g. she knows her daughter only took the dog out for 15 mins, rather than the hour she promised, she knew her husband was planning a birthday surprise as she saw him coming and going with cake, drinks and balloons, she knows when and how long her adult DC's girlfriends are in the house for etc. Presumably they all do (or could do) the same to her.
The whole idea makes me feel very uncomfortable. I've nothing to hide, but I don't like the idea of being monitored. Are most people much more relaxed about it?