Countries don't really do this anymore.
Actually some still do. It's consensus that is not smart to do it, but they still do. Not consolidated democracies like Brazil or USA, but totalitarian governments still finance their excesses printing money and building up inflation.
Back to the monetary slider: I think it might be cool, let's dig a little deeper.
1) The positive side causes inflation, the negative side causes decrease of inflation, not deflation. Also, if you keep going it back and forth, back and forth, this behavior would create an inertial inflation. People will just expect more inflation, because they know how irresponsible their government is. This expectation of inflation, by itself, creates more inflation, as much as people are indexing their payments to a inflation which don't happened yet.
2) As frekk wisely appointed, modern countries don't do it, they know it's harmful. So, let's control it by the monetary civics. The monetary slider will be active only with: State Coinage, Noble Metal Standard, Private Coinage and State Bank.