I believe what you're hearing and what the other replies here might be
missing is that after a few days you will notice less disk thrashing due to
the indexer gathering the complete listing of your file system over time.
After a few days this is not necessary except when there are new programs
installed and fewer changes to the file system.
So in this sense... yes, it does appear to get a little better speed wise
since the CPU and hard drive aren't getting thrashed creating greater
contention while using the system. But you can also turn off the indexer if
you wish. I would suggest leaving the machine on overnight for the first
few days for those that are in the habit of powering down at the end of the
day.