Is there any disadvantage if you don't evolve Charmander in heartgold?
It really depends if you are going to use it to fight like a
pro, use it in the pokelatheon or just keep it as a good team
member. If you want it to be super strong (strong enough to beat my
Charizard =D) you should keep training it until it learns all the
strong moves, then let it evolve. Here is a list of the moves
learnt by level. This is for Charmander-
Level 1- Scratch
Level 1- Growl
Level 7 Ember
Level 10- Smokescreen
Level 16 Dragon Rage
Level 19 Scary Face
Level 25- Fire Fang
Level 28- Slash
Level 34- Flamethrower
Level 37- Fire Spin
IF YOU EVOLVE IT INTO CHARMELEON THEN CHARIZARD.....
Level 36- Wing Attack
Level 42- Flame Thrower
Level 49- Fire Spin
Level 59- Heat Wave
Level 66- Flare Blitz
In my opinion, because I train my Pokemon hard, I would let it
learn all the moves first, then let it evolve. That's what it did
to my Charizard, and it was a success. It now has-
Outrage, Giga Impact, Focus Blast and Heat Wave. It's level
100.