multiple table scan performance

[Samuel Gendler <sgendler@xxxxxxxxxxxxxxxx>]

I've got some functionality that necessarily must scan a relatively large table.  Even worse, the total workload is actually 3 similar, but different queries, each of which requires a table scan.  They all have a resultset that has the same structure, and all get inserted into a temp table.  Is there any performance benefit to revamping the workload such that it issues a single:

insert into (...) select ... UNION select ... UNION select

as opposed to 3 separate "insert into () select ..." statements.

I could figure it out empirically, but the queries are really slow on my dev laptop and I don't have access to the staging system at the moment.  Also, it requires revamping a fair bit of code, so I figured it never hurts to ask.  I don't have a sense of whether postgres is able to parallelize multiple subqueries via a single scan