The other disadvantage (for nonclustered indexes) is that the index can't be used while the rebuild is in progress. Normally rebuilding a nonclustered index makes the table read-only, but the index is still seekable while its been rebuilt (because the old one isn't dropped until the new is complete). Disabling it first means that the index is gone and not usable until the rebuild finished.
Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability