Leaning on the cross...

@Henri Rabagny: Thanks Henri for your comment!

To answer your question, I think it depends on what you would like to achieve and the time you would like to spend when you take the photos directly in B&W. When I did this series, I can tell you that by doing the photos in B&W right there, I found myself paying more attention to the light and the subject itself rather than the pretty colors or the not so pretty ones. I should say also that this was a "first time experience" for me and a way to learn a bit more!