I am yet to use it, but in my research I’ve discovered the following:
You have to. IR film is sensitive to all bands of light, it just has increased sensitivity to the IR range of the spectrum, ie. if you don’t use a filter, you lose the effect.
For false-colour IR film like Aerochrome you need a yellow/orange/red filter that cuts out ALL blue light (wratten #12 or greater, I think I’m going to use #16 for warmer tones).
For B&W IR film like Ilford SFX, it’s recommended that you use a filter that ONLY permits IR. Ilford themselves recommend a #89B filter, but they’re bloody pricey. I’ve seen examples of good results with your average deep red filter, but the less visible light the filter permits, the greater the effect.
Hope that helps.
When there’s actually some greenery about to justify the use of IR film (and once I’ve got the balls to use the Aerochrome), I’ll pop up my own personal experiences.