There are gay dating sites, adult dating sites (those looking for sex), Christian dating sites, Asian dating sites, etc.
They are niche sites, because they focus on some particular group of people.
For instance, they may have age limit or location limit for their members.
So, if you know exactly who you are looking for niche dating sites may work well for you and narrow down your search.
They may help you to find dates within your community or group interests.
In fact, some of the best dating sites out there have free membership option. If you compare paid and free membership sites, the free ones would lose, because they may not offer you some of the best online dating tools and features. No one does anything to make them secure and there is a chance of getting your personal information into wrong hands there.
Summary: the best advice is to find a combination of the two. You test the site to see, if it really works and if it is worth your money. They may either do the matches using their matchmaking system, as it is with e Harmony dating site.