SQL Server: Manually Update Statistics

Is it a bad idea to manually update statistics on every table in a database nightly WITH FULLSCAN? Would this negatively impact performance in any way?

why do you feel you need to do this? Are the tables highly volatile?

It would only negatively impact performance if there is other processing going on during the same time - or is quite useless if you just got done rebuilding the index...as that updates the statistics with a full scan.