I have built my library over the years using purchased music, sounds that I recorded myself and sounds recorded on location for projects that I have shot over the years. I do not use any music from the internet that does not come with license agreement. Supposedly free sounds from the internet can bite you big time when it comes to distribution. You have to have clear title to everything used in your project if it is going to be distributed online or through broadcast channels.
All of my audio clips are all organized in folders by type. I have only purchased one compilation. That compilation was purchased for a video series that I was producing that needed a bunch of funny cartoon sounds and the compilation was less expensive than buying the 50 or so tracks that I needed for the project. I have only used one or two additional tracks in the 12 years since the original purchase. That should tell you how much value I really got from the compilation. On the other hand many of the the sfx, music, and backgrounds that I have saved over the years are used all the time. I have a door slam that I must have used a hundred times.
Here's another tip. I carry around a USB adaptor for my iPhone and a Blue Spark Digital usb mic. It's in the car most of the time. If I hear something amazing I'll grab the sound using RoDe Rec, an IOS recording app. I want to pick up the RoDe IXY stereo mic because it's smaller. If a sound is really interesting and I don't have my Spark with me, I get the sound anyway with just the phone. I've used a bunch of these sound clips in productions over the years.
Hope this helps.
The simple truth here is that the sound you need for a project is the one you don't have in your library. That's the same gag as with fonts. You could trawl the Internet for hours and still come up empty. As Rick said already, copyright can always be an issue, but even if that wasn't the case, you can spend hours to actually match sounds you find on the web or in different collections. different mixing and audio levels you know. So inevitably trying how to record and process your own sounds is a good idea. After all, even today they do foley and ADR on movies using physical methods to produce sound effects timed to the action... They wouldn't do that if using stock sound effects would be an option. And keep in mind their libraries are much bigger than anything you can collect in your entire life, so there must be some genuine benefit to do things from scratch...
Good points from both, thanks a bunch. Matching sounds eh, kinda didn't think about that one. I appreciate the input. Sounds like the safest bet is to roll your own. Maybe record a few practical (ambient) sounds for multiple use and build a library for the abstract stuff as needed over time. Plus i'll get less of that "hey that same sound effect that was in so-n-so's movie".