Using output of pg_ctl for benchmarking?

I just discovered that pg_ctl/postmaster give out stats on the console.
I did a change to postgresql.conf and when I did pgctl restart, from there
on there were some stats. I restarted again and sent the output to
/var/log/pg.log.

QUERY STATISTICS
! system usage stats:
! 40.719759 elapsed 29.342567 user 8.903896 system sec
! [58.287837 user 18.724752 sys total]
! 6175/0 [12352/0] filesystem blocks in/out
! 0/1 [0/2725] page faults/reclaims, 0 [0] swaps
! 0 [0] signals rcvd, 0/0 [3/3] messages rcvd/sent
! 322/672 [802/1410] voluntary/involuntary context switches
!postgres usage stats:
! Shared blocks: 95297 read, 0 written, buffer hit
rate = 0.01%
! Local blocks: 0 read, 0 written, buffer hit
rate = 0.00%
! Direct blocks: 0 read, 0 written

I am the only usr of this system. Any reason why I couldn't use this
output to benchmark?

Any docs online where I could read more on these stats displayed?
For instance whate is "shared blocks"? voluntary/involuntary context
switches?