Ok, I have often wondered this. Why are pre-decrapified files such a bad thing? Surely it just means someone has done the work of decrapifying for you, so you don't have to?
Basically it's because of the possibility that Pescado may need to update decrapify/s3rc at some point. For example, stairs, fences, fireplaces and counters were all not working properly with an older version of decrapify (which was admittedly a long time ago). Now they work fine, but people who are using sims3packs that were decrapped before the update will still have problems.
Of course, the other problem is that it's not quite obvious whether an item has been decrapped or re-compressed by just glancing at the sims3pack. If you run an untouched sims3packs through de-crapify yourself, you know exactly what has been done to the files.
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