Genealogy research ends up being a process of connecting together many individual pieces of information in a logical order allowing you to tell a story. In connecting those dots it is beneficial to leverage work done by others so that you can quickly make progress.
While it is very exiting to come across a relevant family tree created by someone else you should be cautious about over reliance on work done by others.
Family Trees do not all have the same level of supporting research. It can be difficult to know how diligent a person was when they established family relationships in a given tree. As such you will need to conduct some amount of your own research to gain comfort with their conclusions.
A reasonable approach is “trust but verify”. With this approach you can tentatively accept the work done by others as a way to make forward progress in your search but then you should independently verify a few key facts so that you gain comfort the conclusions are true.
Using web based services you can do some verification of facts but my experience has been that primary document research has been necessary to solve the trickier questions. Inconsistencies in spelling of names, ages that don’t line up and divorces make electronic research all the more tricky.