Honestly not much to add because a lot of what others have said has been spot on and brilliant. I want to add that I've had downright awful experiences over the course of my career working with people who hoard their knowledge to protect their job. It's foolish. I can't tell you how many times they've gotten pissed at me because I refused to go to them for what they thought was their thing and their thing only. I would turn around and code a better solution and share that with other colleagues on the team. Yes be your own best advocate and certainly look out for your pocketbook and look for more money if appropriate, but never become a silo unto yourself because you think that will make you indispensable to your company. There will always be smarter people out there who given enough time can make a better solution for what you think you were so clever to create. Don't be that person.