For those of us who crimp our own Ethernet cables testing to make sure the cable operates properly is just part of the process.
1000 foot spools of cable are very useful, and even cheap testers today are very convenient.
When doing long runs of cable you can save yourself some time and footwork by carefully opening your box of cable and finding the beginning, usually it is tied into a knot somewhere.
I cut the knot off crimped a head onto the end and fed that wire through the handle hole. Now I can test a new wire after crimping only 1 head on by putting my tester on the end coming out of the box.
Someone pointed out to me that 1000BASE-T networks have a maximum length of 100m (328 feet), well below the 1000 feet in the spool.. However, it seems to work fine for testing. This is probably not a good idea to use for anything else.