Even on a new firearm, it's a good idea to field strip and lube it. It's just good advice to do so. Remember, all gun oils evaporate, some faster than other, depending on their molecular weight. It's quite possible for a new firearm to go "dry". While it's apart, it just makes sense to inspect the parts for defects or "gunk". I once purchased a new Bersa .380 that shipped from the factory with the firing pin channel packed full of metal shavings, it would fail to fire every 2-3 rounds due to light strikes. That same pistol came back from the factory warranty center with a broken magazine retension spring.
If you strip and inspect every firearm, you'll notice that even most new guns have some residue from test firings. I clean them and relube before I shoot them, which gives me a chance to inspect for manufacturing defects before I set off an explosion in my hands or must use it in a life threatening situation.
The same inspection should be done after any gunsmithing, repairs, or any other time a firearm leaves your possession and returns.
If it's a used firearm, don't even consider shooting it until you've stripped and inspected it. Hell, if possible, field strip and inspect it before you buy it.
