Unlike the genome, which remains essentially static between cell types and over time, the proteome is tremendously dynamic, changing constantly in response to cell-cell signalling and environmental stimuli. Thus even though -with some small exceptions - every cell in your body carries the same genome, the proteome can be wildly different between different tissues and can change rapidly over time
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At the very least, large-scale analysis of the human proteome should allow researchers to tentatively place many of our currently anonymous genes into functional pathways. That’s a step forward for personal genomics: knowing that you have a loss-of-function mutation in a gene that may be involved in cholesterol biosynthesis is a lot more useful (in terms of guiding further clinical testing) than simply knowing that you have a mutation in hypothetical gene C11orf68.