If a character is always wearing the same clothing then the clothes will become an integral part of the character. This can strengthen the design in the reader's memory.
Ex: Where's Waldo's striped shirt, Cruella's oversized coat, the Flintstones outfits, homer Simpson, Buzz lightyears outfit, etc...
So I think that having a character wear the same thing is beneficial to creating an iconic/memorable design, though it isn't realistic.
That said, for comics in particular, it does depend on the genre of story. If I'm reading a slice of life comic, I'd find it strange if the characters never changed clothes. Stories with a realistic edge will probably be better off mirroring reality and in reality people change their clothing regularly.
Or, if your like me, only when personal hygiene forces you to. 