Depends on the RPG, really. Like in Monster Hunter, where your weapons and armor do Elemental Damage/Resistance, has special abilities, etc, and can be upgraded, you never really wanna sell it. Plus, they all look cool and unique, so it's a fun collection-type thing. ^^
In other RPGs, where some things are kinda straight-forward and the weapons and equipment don't really stand out, then sure, get the extra funds.
Usually the only equipment I keep is near the end of the game. Things that might not be the best weapons available, but might provide an advantage based on their elemental effectiveness against a particular boss. Like in Golden Sun, equipping both of your lead Warrior characters with the Jupiter-aligned Excalibur to exploit the final boss's weakness to wind-based attacks. (Due to the most powerful weapon in the game, the Sol Blade, being powerful, but easily resisted by that same boss due to a high Earth resistance.)
The only rpgs that I play a lot of are Pokemon and Digimon World Dusk, and any "equipment" that I get, I keep. Digimon World Dusk has level and species requirements for most equipment, so my lower level Digimon get the weaker stuff until the level up enough to use the better stuff.
Varies on the RPG, and the item. Sometimes I keep items if they are cool and hard to find. Sometimes I just sell them for quick profits and constantly loot. Sometimes I keep things because I know I will need it and be a utility man.
Depends on the game. in world of warcraft I was sitting on bags and bags of old gear and items I kept, whether just for the way it looked when you put it on, or because it had a really gross or horrendous or funny name lol. Never know when you might need to give someone some smelly mold with the caption "Even I don't know where this came from" or something like it xD
Depends on the game. In something like Dark Souls, there's a lot of neat descriptions on the weapons that's cool to read. Or like Tales of Vesperia where you need to keep original weapons so you can forge special ones out of them. But on the other hand sometimes there's just games like Final Fantasy in which case yeah I'll sell old stuff.
Depends on the game, but typically, I keep them. The one time I didn't keep specific gear, I lost out on a massive upgrade for a specific set because it was incomplete and didn't mention it until I got the last item.
but for example: on Five Nights at Fuckboys 2, you need a stick to get toy bonnie out of a vent. after you do that you think the stick is pointless right? wrong because if you DON'T sell the stick and you go for the true ending the stick (somehow) evolves into an extremely OPed weapon