The temporary confidence boost that BlueMushroom64 spoke of might soon go to shambles if you want to speedrun the game afterwards, as you will have to relearn all of your safety-oriented approach. Confidence or not, speedrunning is for a great deal based on muscle memory of specific strats. In my case this confidence boost would soon turn into high expectations and disappointment, since deathless and going fast are vastly different.

On the other hand, if you think a deathless run is fun, go for it. Having fun makes learning a lot easier. Just don't expect your deathless experience to translate very well to anything different than the exact thing that you practiced.