You know, statistics are both fun and painful at the same time. Some people truly enjoy playing with numbers though, to our benefit.
According to Frank Seravalli, tonight is a huge game for the Leafs. He explains it in a simple graph here.
To make it simple for you, the blue part is favorable for the Leafs, the red is not. Basically, if the Leafs win in regular time tonight, their chances to get into the playoffs will jump more than 13%. However, if they lose in regular time, they lose 12% odds. The other games displayed also have an impact on the Leafs' odds, but a lot less.
Toronto has 36.6% chances of getting into the playoff before tonight's game. Losing 12% or winning 13% will dramatically change the odds. The Lightning is far from an easy prey, but Babcock's gang can do it.