Compiled trees (regardless of the compiler or the book, site, etc.) should not be your only source for a fact, relationship, date of an event, etc. These trees can lead you to other sources and give you research ideas, but do not simply "copy it down because you saw it online."
At the best, compiled trees provide references to original source materials.
At the worst, they are completely incorrect.
The truth is that most are somewhere in between. Use them as clues.