Is there any benefit in limiting the number precision on a surrogate PK in Oracle? I'm reviewing some DDL that creates surrogate primary keys of type NUMBER(38).  When I first looked at this I thought it was a problem because 10^38 is a HUGE number, much much bigger than the number of stars in the universe or all the grains of sand on earth.  But I've come to learn that this doesn't matter in terms of how the numbers are stored.  And there doesn't seem to be any other options than say using a float type which I'm not really ready to seriously contemplate.  Here are some references about those facts:


Is there any point in specifying the precision and scale of a number for a foreign key?
Oracle integer to number conversion
Oracle Datatypes Reference


Given that, it would seem that it's pointless to bother with declaring a limit on the size of the PK i.e. just use NUMBER (which apparently can hold 40 digits.)  The only answer that I've seen is that you should do it for consistency.  But for a surrogate PK, the only thing it needs to be consistent with is itself.  What I mean is, if we set a limit, it's going to be something larger than what we would possibly reach so it seems completely pointless.

One piece of this I'm not sure about is whether the declaration could matter for indexing.  I think it probably doesn't for the most common approaches but are there any indexing strategies that might take this limit into consideration or use more storage because the column is not limited?
Just use 

my_key number not null


If you are generating the primary key using an Oracle sequence (PS: you should), you are guaranteed to get integers so you don't have to have Oracle checking precision, etc. if you specified number(7,0) to specify an integer with up to seven digits.  

And then if you ever exceed 7 digits, not a fun day to fix that.  As the links you've referenced above mention that Oracle only uses enough space to store the number, no need to worry about how much storage is being used; and therefore you don't have to concern yourself with indexing of the columns holding the primary and foreign keys.

The only time I would specify a fixed length integer would be if the primary key was an intelligent key such as a USA social security number, but intelligent keys are a bad idea too.