My tree on Ancestry is Private and all people who can view are Guests.
Would never allow anyone to edit any part of my tree which has taken hours and a fair bit of money to get the accuracy I have.
On GR I have given people permission to view my tree only to find ALL my family suddenly on anothers tree even those not related. For instance my Irish Family would not need to appear in the tree of a distant relative of my English Tree. My Mum was Irish so my fathers G/g/g/grandparents would have no connection to her whatsoever.
After this happened a couple of times, I now no longer give anyone access to my tree unless they ask me specific questions about a specific ancestor and then it will take a few back and fro messages for me to ascertain the connection is right.
There are far too many people out there who think this is a cheap hobby and look to use others hard work to build up their trees. I am more than happy to share my research and copy any BMD's I have for most people but not for the 'tree scrumpers' or those who wish to have as big a tree as possible.
I am now going to sound very mean: You only have to look to see how many people repeatedly ask for look-ups on here and GR. I am more than happy to help with 'free' look-ups for people but there are some who have been doing it for years at others expense. I currently pay out £100.00+ pa for Ancestry and around £80.00 for FindMyPast (both full for my uses within the UK). Now I know this is a lot of money but this is my hobby and all hobbies come at a cost. Even when I first started I realised that I would need to take out membership to at least 1 genealogy site and went originally for Ancestry (then succumbed to FindMyPast). But there are some out there who do not even go for the free trials and then use that time constructively.
SORRY TO RANT - I am a pensioner on a limited income, but I budget to find this money.