I guess that ,,poupar" means save for example money, ,,not to spend them but keep for better times" and ,,salvar" means save for instance someone's life? Eu poupo dinheiro desde ano passado - I save/keep money since last year. O homem salvou a vida da mulher - The man saved the woman's life? Or there is no difference between these two?
There is a whole lesson here I think. Saldo means balance as in bank balance, or the balance left on my phone; however it also means markdown which means sale (as in a sale). A savings account is poupança but also thrift (savings). The stores tout poupe (save) on this or that, and one store has a loyalty card they call poupamais (save more) while barato means always cheap, inexpensive, low-priced. Melhores preços = best prices. Descontos = discounts.
Uh, "he always spares money"? That sounds like he saves it from death... so in that way he is still saving the money. :)
Central banks routinely collect and destroy worn-out coins and banknotes in exchange for new ones. This does not affect the money supply, and is done to maintain a healthy population of usable currency. The practice raises an interesting possibility. If an individual can steal the money before it is incinerated, the effect is the opposite of burning money; the thief is enriched at the expense of the rest of society. One such incident at the Bank of England inspired the 2001 TV movie Hot Money and the 2008 film Mad Money.
Anyway, poupar in your example of "spare time" (for instance, In my spare time I respond to comments on Duolingo [and annoy everyone]) is an adjective and not a verb so is better covered by the PT words of, tempo livre, or sobressalente (spare parts = peças sobressalente), or, disponível (available), or even... "extra" (just for loanword fun).
While poupar tempo means save time:
But, as with all translations, some colloquial phrases like "spare change" just do not translate word for word.