Same deal as New Year's Resolutions really; it's a tradition that gives people a kick up the arse to better themselves. Some people simply need that kick and it can have reprecussions long beyond 40 days and 40 nights. For example, I gave up fizzy drinks for Lent once...13 years later and I still haven't touched one.
We live in an age where people are eating worse than ever so a tradition that has, over time, effectively became 'stop eating/drinking [bad food/drink] for 40 days' is a-okay with me.
It often does have an impact... during my first Lent, I was an adamant Marxist-Leninist who admired Joseph Stalin, and I gave up visiting and post on a far-left message board, and my activity on that forum diminished after Lent. (
And after that Lent, instead of singing canticles to Uncle Joe, I become a conservative Catholic who now has an uncompromising obligations to vote for the Republican Party because they are against abortion. I still haven't found an alternative political ideology that filled the vacuum, so I still consider myself a "Marxist-Leninist" if I had to declare an ideology since it is still the political philosophy that I can defend most facilely, and it still resonates with my moral sentiments.) In retrospect, I really did believe that sacrifice had great significance, since Christianity is not a political ideology whose ultimate end is to influence citizens or the government or arouse disenfranchised masses in order to acquire political power in order to affect the social order. Political ideology always intends to impose its will upon others, for better or for worse. But an import element of being is Christian means being Christ-like: humbling submitting oneself to do the Father's will and emanating His love through one's sincere and pious example while being joyous and peaceful under the Spirit's influence, not trying to persuade or ridicule those who do not yet adhere to your creed and ideology. For this and other personal and intellectual reasons, I am also dismissive of the value of Christian apologetics; indeed, I experience greater intellectual satisfaction reading the works of secular philosophers, such as Karl Popper, David Hume, and Peter Singer, especially Hume, who eloquently presented arguments that cast doubt on the existence of God. Saint Augustine is probably the only Christian writer (although I haven't read that much) who I find his apologetic/polemic work engrossing.
Certainly, one should not merely be lukewarm, and merely see Lent has a traditional occasion for one to acquire the impetus for self-improvement in the secular sense. Indeed, one of the most poignant passages during the period of my conversion is Revelation 3:16-17, which is Christ addressing the Church of Laodicea. One's sacrifice should be chosen to get chose to God and an expression of one's fervent love for Him; it should not merely be an empty gesture.