Timing web requests is possible in curl using the -w or --write-out flag. This flag takes a number of different options, including several time based options.
I'm a proponent of automation, so when I find myself running the same commands over and over I always look for a way of wrapping that in an alias or script.
Grep is a really powerful tool for finding things in files. I often use it to scan for plugins in the Drupal codebase or to scan through a CSV or log file for data.
For example, to scan for user centric ViewsFilter plugins in the Drupal core directory use this command (assuming you are relative to the core directory).
Part of the process of putting a new site live can be moving DNS entries around. Prior to doing this it's a really good idea to sort out the Time To Live (TTL) of the DNS record so that when you do change DNS entries you aren't waiting around for a day for the DNS to sort itself out.
Whilst it is possible to view the contents of an SSL cert from within most modern browsers I occasionally find the need to use the command line to find out the same information. I find this useful when renewing certificates as browsers can occasionally cache certificates for longer than expected, causing false results.