Most restaurant or premade Cesar salads are not that healthy and have just as much calories as other options. Lettuce in itself is basically just water with a small amount of nutrients so eating it does basically nothing (positive or negative), for some people it might help with satiety by giving you a full stomach feeling but personally I'd rather not chew on greens for hours like a ruminant and prefer to drink ample water alongside/after my meal for the same effect while making sure I eat plenty of vegetables for the actual good nutrients etc.

Anyway yeah these Cesars from restaurants etc are doused in sauce and have a bunch of calorie-dense ingredients so they're not always a great choice (but fine to have as long as they fit your calorie allowance, just like anything else). Just make sure to balance your carb/fat/protein ratio and not go over the calories, but otherwise just eat whatever you want!