One of the quickest and most convenient ways of finding out whether or not someone is dating material for you is to know that all members on a site are of a particular religion. This is certainly why religious dating sites are proving to be increasingly popular nowadays.
Members of certain religions prefer to date others with the same denomination. This just makes things so much easier in life. The potential date would have far more in common with them, than if they were from an entirely different religious background.
Sites like Catholiconlinedating.com are catching on a storm and this really will be the online dating sites of the future.
For those people who do not follow a religious persuasion or have been long since lapsed, online dating sites would also be able to appeal to agnostics and outright atheists.
These examples of dating sites all help to cut out a lot of the unnecessary hunting around. If you know the person has been brought up with the same beliefs and traditions as you, this can take away a lot of pressure at the start of any relationship.
The only negative to this approach is the fact that this does tend to categorise people a little. We do try to live in a multi-cultural society and so this is taking a step back from this. At the end of the day though, at least this option does allow people to make up their minds for themselves.