Bottom line
Telecommuting lets you complete certain inactive duty training away from your Home Training Center (HTC), at times other than scheduled drill. It only covers Additional Training Periods (ATPs) and Rescheduled Maneuver Periods (RMPs), never your regularly scheduled IDT. You need your CO/OIC/I-I/OpSponsor to approve it in writing before you do any work, and you must submit the paperwork (a signed request, a completed DD Form 2946, and a telecommuting log) within 5 working days of finishing each period.
What it means for you
If your command agrees, you can knock out an assigned project from home and get credit for it as an ATP or RMP, without driving to the HTC, cutting orders, or spending travel money. It is a privilege the commander can take away at any time, not something you are owed. There are firm limits: no more than 36 ATPs and RMPs combined by telecommute in a fiscal year, at least 4 hours of work per period, and no travel or per diem. You must be in a satisfactory drill status and fully qualified in your Billet Military Occupational Specialty (BMOS) before you can telecommute.