What does "sudo nvram boot-args="debug=0x10"" do to my Mac?
sudo nvram boot-args=&quot;debug=0x144&quot;

This is a combination of kernel debugging features that will show you extra information about the kernel's processes, which can be exceptionally useful if a system is experiencing kernel panics. Another option is to use debug=0x14e, which will display even more logging options. The primary use for this is that it enables old-style kernel panics that show scrolled text on the screen about why the system panicked, instead of displaying the gray backdrop and the message to merely restart your system. Alternative debug options are the following, though these will likely only be useful to kernel programmers:

0x01 - Stop at boot time and wait for the debugger to attach
0x02 - Send kernel debugging output to the console
0x04 - Drop into debugger on a nonmaskable interrupt
0x08 - Send kernel debugging information to a serial port
0x10 - Make ddb the default debugger
0x20 - Output diagnostics information to the system log
0x40 - Allow the debugger to ARP and route
0x80 - Support old versions of gdb on newer systems
0x100 - Disable the graphical panic dialog screen


Source: Boot argument options in OS X
ddb is just a debugger. It's absolutely safe to enable those kinds of modes to collect information once you experienced system issues.