The position of whip plays a very important role in government. They are responsible for making sure enough politicians show up to vote. A simple miscount can lead to a piece of legislation being defeated or amended. Such embarrassments have happened from time to time like in the Ontario legislature when the NDP stuck in an amendment to the city of Toronto amalgamation legislation. (3) Conservatives MPPs had become so bored with the opposition filibuster that they didn't realize it was time to vote.
These days the job is particularly difficult for Karen Redman (Liberal Whip) and Marcel Proulx (Liberal Deputy Whip). Normally in a minority government, one of the opposition parties will support the government or they will topple. The Liberals are in a situation where they want to oppose government legislation while allowing it to pass.
Today's vote on amending the budget was carefully crafted to insure that the NDP and Bloc would vote against the amendment. The amendment was defeated by a vote of 202- 7. For good measure only the seven most relevant Liberals showed up for the vote: Dion (Leader), Ignatieff (Deputy Leader), Goodale (House Leader), Jennings (Deputy Leader), McCallum (Finance Critic), Redman (Whip), Prolux (Deputy Whip)
The vote on the actual budget will be much more difficult. The Bloc and the NDP will be voting to bring down the government. The Liberals will be taken more seriously by the electorate if more than 7 MPs show up to vote. Adding more opposition votes will require careful counting from Redman and Prolux. Accidentally toppling the government would be more embarrassing than this sessions Liberal practise of showing up in order not to vote.