If you're a newer player though btw, you might at first get punished often for spot dodging and get discouraged from spot dodging ever again in your career, but it's actually a good option, and you will see high level players (I guess specifically in this case Yoshi) use it a decent amount, but obviously nothing in this game can be used constantly with little regard to punishment, spot dodge is clearly a case of this. Most of the time it's better to roll away if you're trying to avoid being hit if you like wiffed a f-smash or something, but spot dodge is just another option, like jabbing immediately after you're wiffed f-smash, or just flat out jumping away, it really just depends on the level of play to make the right decision.
You know, much of this game is about doing moves with low lag (with Yoshi this is like b-air, any aerial started well before you hit the ground (l-cancel will be quicker), neutral 'B', etc.) just far enough away from your opponent (spacing) so that you can get out of the way of their counterattack JUST in the nick of time and as a result you will be able to counterattack the counterattack. If you're newer, don't underestimate the gravity of this paragraph, it's quite honestly the most used tactic at professional tournaments. You need only see players like Azen and Mew2King (if you're new these guys were like the best players back in '07..) doing things like this every 2 seconds in tourney's to see how often and necessary this kind of mindgame is. Spot dodge is a good way to quickly avoid things and set up for a counterattack, nuff said. Literally you can walk into the middle of the stage with Yoshi, neutral 'B' at thin air at just the right distance away from your opponent, they'll try to run and dash attack you or something, you'll spot dodge and either immediately hit them back or chase their roll they they will likely do after wiffing the dash attack.