A multi-tool is the do-everything item that earns its place in almost any kit by being competent at a dozen small jobs. A good one folds pliers, a knife blade, screwdrivers, scissors, a bottle opener and often a small saw or file into a single pocket-sized unit. It is what you reach for when something needs cutting, gripping, tightening, trimming or prising and you do not know in advance which. Its strength is breadth: it turns one tool into a portable workshop for the fiddly, unpredictable problems that come up during a repair, a camp setup or a breakdown.
A folding saw does one job and does it far better than any multi-tool ever will: cutting through wood. A dedicated pruning or bushcraft saw has a long, coarse-toothed blade that folds safely into its handle, and it will get through a branch, a fence rail or firewood in seconds where a multi-tool's tiny saw would take an age and blister your hand. It is bulkier and single-purpose, but for clearing storm debris, processing firewood or any real cutting task, it is the right tool. The two are not competitors so much as different scales of the same idea — precision versus power.