* The ids will grow faster, and they will be large even on small tables. It may be a bit irritating if you have a table with just 5 rows and the ids are 5, 6, 7, 12654, 345953. * Bottleneck? Using a single sequence was said to be a performance bottleneck in Oracle. I didn't notice a performance difference then and I doubt it would be one in PostgreSQL, but if in doubt, measure! * Doesn't work with IDENTIY - those columns always use implicit sequences. * currval() is pretty useless with a global sequence. But I basically never use that anyway.
* you will have to pay attention to rollover/overflow situations more quickly.