A foot brace is what makes the canoe an extension of your body. It let's you lock in, BE the canoe. You wouldn't use it it all the time but I'd much rather have the brace available. It also helps my knees stay happy as there are more leg position options.

FWIW - I had absolutely no clue how to use one for the first few years. Now , if the canoe I'm using doesn't have one I miss it tremendously.