Hi Murph and welcome to fishkeeping and the UKAPS forum.
Like most things its never black and white it really depends on what you are trying to achieve and your budget.
A filter can perform three types of filtration.
1/ Mechanical:- The physical removal of solid matter from the water. Rather obviously the type and size of this organic matter (fish poo, dead plant leaves. etc) depends on the bioload in the tank and the size of its residents and may determine the maintenance regime that you will have to perform to stop the media clogging thus rendering the filter redundant.
2/ Biological:- Often refered to as the nitrogen cycle. As organic waste breaks down it produces ammonia, this feeds the bacteria in your filter who turn it first to nitrite and then into nitrate. This is done by two different types of bacteria which cohabit on your filter media and every surface within your tank, i.e. substrate, tank sides, hardscape, filter pipes, etc etc. The larger the surface area the bigger the bacteria colony which is how some of the pourous ceramic media (sintered glass, matrix, lava rock, alfagrog, ehfi substrat pro, etc. etc) comes into favour with so many. Ammonia and Nitrite are highly toxic to fish and ammonia is one of the triggers which causes algae to bloom so there quick removal is very desirable. The larger the bacteria filter colony the easier it is for them to deal with ammonia spikes.
3/ Chemical:- This type of filtration is not strictly necessary but can come in handy depending on what the aquarist is trying to achieve. It allows the user through specific media types to target the removal or addition of certain substances (or group of) from the water by specifically designed media.
It must be remembered that there is a cross over whereby all media employed performs more than one of the functions listed above. For example bacteria will colonise every surface so ceramic noodles which were intended to mechanically remove large pieces of detrius will also function biologicaly to some degree or other. Its also why you can get away with using just sponges in your filter as they perform the two most important functions that you need i.e mechanical removal of waste and biological breakdown of it.
However you can boost your filters efficiency by employing specific media types which suits the exact demands of the application that its used for but its often a trade off with a reduction in flow.
Personally I use ceramic noodles/rings first as this helps to stop larger debris clogging up the next layers therefore performing a mechanical filtration function. After that I have either matrix or ehfi substrat pro (I have more than 1 filter) which is aimed primarily at the biological filtration. After this I use a fine filter sponge followed by a filter floss pad both performing further mechanical filtration functions to get the tiny particles out of the water. Then finally I may use other more specific media as and when required to chemically alter the water but currently I have Purigen in there (which arguably strictly speeking isn't chemical media but thats a whole other subject) which hopefully removes any traces left of ammonia.
Hope this helps.
Regards, Chris.
on fact they are probably detrimental, as most remove nitrogen and phosphate which we want in the tank for our plants 
