The files kept on Ancestry's data base are often much more complete than on other free sites. If you have never used Ancestry you wouldn't know that.
Everyone knows that the Trees on Ancestry are prone to errors and are never considered a "source" written in stone, however, the Gallery section on each profile on an Ancestry Tree holds much useable information. That is the treasure trove that offers photos of plat maps, family research, old photos, stories and biographies that can give valuable clues to every researcher. To think that a free site should be used instead a paid site is just ignoring the wealth of material contained on Ancestry. Family Search and Ancestry are not the same at all.
I always try to link the sources on Ancestry directly back to those records when possible. Sometimes Ancestry will not allow you to copy and paste items due to copyright issues, but the place where the record can be found, volume, page, etc is always provided. The link to an Ancestry Tree can only be placed down in the Sources Section on WIKI but it should only be a way for a researcher to go to the Tree to look at every bit of data available on each ancestor's profile. I can't imagine not being able to do research without it although I use Family Search, My Heritage and Rootsweb. I find more errors on the "trees" on those sites than on Ancestry. Always look at the length of time a person has been a member on Ancestry. Those older trees are the least error prone due to the ethics of genealogy research that were used "way back then" and the newest folks are not careful and slap anything and everything on their trees. The end.