There was ever a non-Christian who asked me, "why give the money to your church, when other areas seem to require more investments (in the likes of the allowances for our parents and even our contribution to the world)" I was dumbfounded upon hearing that, yet as Paul had put it, Christians ought to be able to defend their faith in the lights of such challenges, which unfortunately is one trait many young Christians today lack. Frankly, I was desperate to think fast and give an immediate response the best which I could manage so that that short period of silences would not give the impression that I was uncertain. The fact is that, I was not, for that my faith lies in the all-powerful God, of whom has no space for me to be uncertain about.
(I stopped here at least 2 hours ago, and now I've lost the mood to talk about this issue already.)
Anyhow, the reason why Christians tithe is far more than the monetary reason which most people see. The churches do not require anyone to give, rather it is pretty much a voluntary act and the rationale behind this, for myself at least, is to give an acknowledgement to God- a declaration of our faith to the world that we do not live on bread alone, but rather drink from the river of life which comes from our Lord alone. That is, we do not rely on money, but rather only on our all-powerful God who provides us with more than sufficient. An affirmation of our faith.
As for what the churches do with the money, it has no implication with the individual's act of tithing. Regardless, most churches commit a significant amount from that collection to charities and other underprivileged prospects in the society. For one, I heard from Pastor Fuman that 80% of the collection from the tithing in St. John's Chapel goes to such function. 20% of which are then used to support the personnels in the church. Of course, there are other churches who practise otherwise thus giving the world a distorted view of Christianity, which should never have been the case. Myself, for instance, has zero liking for prosperity gospel anyhow-
Self-claimed people who benefit themselves by taking majority from the tithing to purchase luxury items or even cars or houses. THESE, are not the Christians we aim to be like.
Ps. If giving money to the parents is more important than tithing, then what's with the offering buddhists put into the offertory box each time they visit the temple. Let me emphasise once again, my security and my sufficiency lie in God and God alone (I'm not saying that I won't contribute to the family, but let's draw the line proper- when you give one who does not manage, and when you give others who might be given a leash of new life due to that dollars and cents from us.)