This is a tricky question because you will have to answer this question depending on the situation.
There are a couple of points that should be kept in mind before choosing to depend on a local's point of view or before excluding a local's point of you.
1. Do you have adequate knowledge about the location?
If you have adequate knowledge about the location, there is no need to depend on the locals. You can still ask them for they are suggestions but work on them only if you think it is a viable option. This means that asking the locals will only help you extend your knowledge base, and there's no harm in learning something from them. Another point to be noted in this case is that if you have adequate knowledge about the location, you will be in a position to determine whether the local's suggestion is good for you or is it a risky option.
2. Is your map reliable?
There are many online and offline maps available for travelers. You are the one who is choosing the map, and so, it is your responsibility to be sure that not selected map is reliable or not. If you are sure that the selected map is totally reliable, there is no need to rely on the locals for their suggestions. However, if there is any doubt in your mind that the selected map is not totally reliable, even though it is the best map available for you, be sure that you take advice from the locals and act accordingly. It is important to understand that the advice given by a local will definitely be better than an unreliable map. So think about it and accordingly decide whether you should opt for a local advice, even though you have a map, or not?
A fellow traveler who has seen a lot of the surroundings of the location you are planning to visit you should rely on their suggestions. However, it is important to understand that if they have been to the location a long time ago, there might have been a number of changes at the location. With this being said, relying totally on their suggestions and backfire. So be careful and think twice before acting upon their suggestions.