Unless you have a specific effect you're trying to achieve with filters, there's no reason to use one, particularly as most modern digital cameras will have their own UV filter covering the sensor.
The main argument for purchasing a UV filter is that it can provide additional protection for the front element of the lens. This might be a consideration if it's a boisterous party where people will be bumping into you, or beer is flying around. The small outlay for a UV filter is better than replacing a lens.
The main thing you'll have to consider will be the light falling away as the party progresses and there are three things you can do to combat this:
- Provide your own light source - invariably this means adding flash. The drawback to this is that it can make your photos look flat as the extra light swamps the foreground, leaving the background dark. Once the sun goes down, you won't really have an alternative though.
- Increase the camera's sensitivity - this means increasing the ISO setting on your camera. You can either leave this to the camera if it has an Auto ISO setting, or adjust it manually. The downside is that a higher ISO setting will introduce more "noise" into the image but that may be an acceptable alternative to flash around dusk.
- Use a faster lens - around f/1.8 or better. The larger aperture will ensure that more light reaches the sensor, resulting in higher shutter speeds. Unfortunately these faster lenses tend to be more expensive although there are fast primes available for most DSLR camera makes.
Invariably it will come down to using a combination of all three methods. Stick with a prime lens throughout the event, bump up the ISO when the light begins to fade, and add flash when there's no natural light available.
A polarising filter is useful for cutting down on reflections and boosting the intensity of colours, but it will reduce the amount of light reaching the sensor, typically by around 2 stops. So it's worth getting one for landscapes but it will be useless for your party. If you do decide to get one for future use, make sure it's circular so your camera can automatically adjust the exposure.
