you can do a lot of things, in fact most things without proxies. You NEED proxies for posting and you want private proxies only. Ill put a link below to all the sources I use/recommend
As for scraping you can do it without proxies, you just have to go SLOW with a massive delay in the detailed harvester. You can scrape proxies and use these scraped public proxies for scraping in general, but thats about all they are good for.
For anything else that you need proxies for you want private proxies.
Most generally, if you are going slow enough though, you don't need proxies for a large amount of things just keep connections at 1 or 2 and if you are using all the same domain (like in an email grabber for example) then you just need a massive delay.
So the only real issue where you need need need to protect your IP is posting, fast poster, contact forms etc... Otherwise proxies really boil down to allowing you to go faster as no proxies, for some things, like scraping, can be very slow.
Providers:
http://scrapeboxfaq.com/scrapebox-proxies
Video explaining the rotating proxies mentioned by
@Nargil