Ofcourse, there are some downsides of having bigger sized datafiles.

1) As everybody said managability becomes a concern.

2) As many will not aggree to this point..and had been detabe on this with no conerete outcome.

The downside is...
OS will always try to allocate, contigious block of Memory on harddisk...and if say while creation of datafile if you give size 2 or more GB, then OS cannot allocate conitigious block to it...rather peices of small blocks will be allocated..

This would have indirect imapct on overall performance of the DB, as its easy to read the Data which is stored as Contigious Block of Memory on harddisk rather than dispersed/scattered blocks of Memory segments.

So its always benificial if you have smaller datafiles, in the perspective of physical reads.

That however small might be the duration to have the data read from scattered Memory blocks to that of Contigious Blocks...it will be significant, had it been a very large DB, or had it been a DB where active Transaction are very large.

Abhay.