The four major "latin" languages lie on a continuum, with French and Spanish being the most different. Italian and Portuguese are most like Latin, but Italian is closer to French, and Portuguese is closer to Spanish. This happened for geographical and historical reasons; Portugal borders on Spain, and France and Italy are neighbors (France and Spain less so, despite a common border, because of the Pyrennees.
French deviates the most from Latin, probably because of its proximity to Germany; the French laisser and the German lassen both mean "let." It's worth knowing Latin to know in which respects a French word has Latin versus non-Latin (e.g. German), roots. Likewise, Spain historically had some Celtic and Arabic influences, and where Spanish deviates from Latin, it's probably in one of those two directions.
My Portuguese teacher told me that he felt that a knowledge of Latin was of help to students studying the two more "proximate" languages, Italian and Portuguese, and of some help for the two more "remote" Romance languages. And learning one would make it easier to learn a second. He also said that he wouldn't learn Latin just to learn one romance language, but the effort would be worth it if you wanted to study "several."