Do You Guys Use Proxies for Testing?

Hey guys,

Do you ever use proxies when testing out a new MTG deck?

I usually find it useful when I want to try a few cards before actually buying them. It makes it easier to see if the deck works the way I expected, especially when trying different builds.

Just curious how everyone else does it. Do you use MTG proxies for testing, or do you normally build the deck with cards you already own?