What is the opinion on doing gyms out of order? Do they serve no purpose or do they provide for exploration and replayability?

*In red and blue you need to beat koga to get to cinnabar island
*You need to beat brawley before norman
Fun fact: Wallace has extra dialogue if you haven't beat Winona
"There remains but one Badge to obtain in Hoenn. If you wish to challenge the Pokémon League, you must obtain the last Badge from the Gym in Fortree