I've programmed for a long time. One of the best programmer's I've known actually had his own debugger. He was an OS kernel developer and carried the debugger with him from job to job; we were working on the new operating system at IBM that would become AIX. He was a bit of a nuisance in the large development organization because he would wander around the kernel in his debugger fixing code before others had even noticed the defects.

We were working on a distributed file system, and I had complained that we couldn't be expected to finish on the same deadline as the hardware device driver teams and the network stack teams. How would we even develop our software if we didn't have any working communication between machines? Well, my friend came to the rescue and wrote the kernel support for the NIC and a comm stack up to the level of UDP (having a debugger helped).

Eventually, the managers of the other departments that wouldn't cut my team any slack on our schedule started coming around to ask us for help because they were falling behind schedule. They were responsible for the official development of the network device drivers and networking, and it turned out they didn't have a working kernel debugger like we had (thanks to my friends personal one), so they had fallen behind schedule while we were already making good time on our distributed file system running on top of the our own hacked together temporary device drivers and networking code. I had to lend the teammate and his debugger to the other two teams to help them with their schedules.