I have watched anime for quite some time now and started watching subbed, when I realized that the animes I liked were way ahead in the original version. Like a couple of hundred episodes for One Piece as an example. I got used to reading the subs in my peripheral vision. There may be some instances where I have to do a double take if there is an unusual word, but that’s very rare. English isn’t my first language, but english subs are more easily available. Outside of anime, I always choose the original version with subs as well because it feels more natural to me and I’m used to reading subs anyway. One good example is Sopranos, where the dub in my language doesn’t have any Italian accent whatsoever. The great mafia atmosphere of the original gets totally lost that way.
That aside I totally get watching the dubbed version. Today in times of simul-dubs you don’t have to wait for years at a time. You can watch dubs as background noise. The voice actors are usually great, even if not as consistently incredible as the originals. I always watch dubs with my family and friends, often shows or movies I already watched subbed. Watching something together for me isn’t about the show alone but more about experiencing it together. Watching subbed would defeat that experience as you couldn’t talk to each other as easily as with the dubbed version in your native language.
TLDR: alone I watch subs for the original experience, with others I watch dubs for the experience of watching together.