Mutation can affect meaning, for example the word "ei" means "his" when followed by soft mutation and "her" when followed by aspirate mutation (and the identical sounding "eu", meaning "their", does not cause any mutation):
ei chi = her dog
ei gi = his dog
eu ci = their dog
I think if you want to learn a language you should try to learn it properly. Mutations may seem "exotic" to speakers of other languages, but they're just as much a part of Welsh as, say, prepositions or verb endings; would anybody question whether it's worth bothering about learning prepositions or verb endings?