Hot water will clean better than cold, but hot means somewhere close to 130°F (50)C). There's no benefit to going hotter, and could be problems. In any case it's not the water that cleans, it's the detergent in the water. One advantage of washing hot, is that the parts will retain heat when removed, and dry faster and more completely than with cold water.
Either way, whenever you clean with water based solutions, be sure to rinse completely and thoroughly, so the parts don't dry with residue of your detergent or cleaning agent inside.
On serious argument against boiling is that not all parts are 100% metal. Many of the plastic and rubber parts on bike components will melt or warp at temps above 150° F.
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