Is there a specific reason for using dnsmasq as opposed to adding entries to the /private/etc/hosts file and leaving DNS pointed to your ISP?

Is there a specific reason for using dnsmasq?

You could simply add entries to your /private/etc/hosts file leaving DNS pointed to whichever ISP you happen to be connected to. Here's how to do that using Terminal:

sudo nano /private/etc/hosts Enter you password when prompted.

Add any additions at the end of the hosts file (a single entry per line), for example:

127.0.0.1 local.dev

Control + O and then enter to save the file within nano. Control + X to exit nano.

You'll than need to flush the local DNS cache using: dscacheutil -flushcache