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Intermodulation ratings determine how the amp deals with multiple strong incoming signals. If you have two or more strong signals coming into the amp, they produce signal byproducts (undesirable internally-generated signal artifacts) that potentially act as interference on neighboring channels.
If your situation has a combination of very strong and very weak signals that you are trying to get, the intermodulation byproducts from the strong signals might clobber the weaker channels. The intermodulation rating on your amp gives you an estimate of how strong those intermodulation byproducts will be relative to your strongest signal.
Look at the signal power difference between the strongest and weakest channel you are trying to get. If that difference is more than 44.8 dB (that's 60 dB - 15.2 dB since you need a minimum of 15.2 dB of signal margin to lock on to a digital TV signal), then there is a chance that your amp may be the limiting factor in picking up those weaker stations. Things may or may not work depending on your particular situation (intermod products will vary by frequency and strength depending on the frequency and strength of your strongest signals).
If all of your desired signals are close in power, then this is not much of an issue.
A high intermodulation rating on an amp is generally a good thing, but it doesn't tell you anything about the noise figure of the amp.
If you need to pick up distant / weak signals (no strong signals present), a high antenna gain and low pre-amp noise figure are the most important parameters to target.
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