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Like most things in life there are different types and levels of quality in filters...UHC/OII/coloured/polarizing etc.
A good filter will block out a particular wavelength(s) of light and only let pass through the observationally desired portion. Different filters let through (filter) different wavelengths of light. This makes it easier to see some objects as only the specific spectrum(s) of light that is of interest are passed through the filter. Think sunglasses.
For example, filters can be employed to block out the specific wavelengths of light given off by sodium/mecury streetlights...hence improving the view. Another example would be the use of a colored filter to pull more detail out of planet observations.
Having said that, no filter can ever replace a dark sky for DSO work! The light given off by the streetlight will make getting your eyes dark adapted impossible and so while they can aide the blocking of the non-Astronomical they will not turn a backyard into the Outback.
I actually find that DSO filters work best in a dark sky situation...while this may sound counter intuitive, a good filter will discriminate against the light you don't want and thereby make some objects "pop" right out.
Maybe I am just getting lazy or have becoem a bit of an observing snob but I tend to choose to view bright objects not as impacted by the light pollution from my backyard saving my DSO cravings for when I am under a darker sky...and with a DSO filter amazing.
There are many good articles on Cloudy Nights website...many written by an amatuer observer from Nebraska (David K)...well worth a read if you are interested in filters. Clear Dark Skies!
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