I have to do a lot of calculation on the fly. When I'm on a business call and someone gives me up-to-date metrics I frequently have to translate that into numbers that make sense for my business. (e.g. If I'm on the phone with a vendor and someone tells me their unit price is $1.44, I need to add that to my COGS, subtract the current unit price, and multiply by monthly or annual capacity to figure out how that's going to affect costs.) I can do this by touch while I'm talking in 2 - 3 seconds if I have a numpad. If I don't, I need both hands and roughly twice the time per calculation and I need to double-check I typed things right because the numbers aren't aligned quite the same way on each keyboard I use. It becomes a noticeable drag on productivity when I'm performing more complex ad hoc calculations for reports or presentations. I used a macbook for years and won't do it anymore. Linux on a computer with a numpad is the only way for me to go now.
IP addresses and IDs. Very satisfying to quickly bang out multiple numeric strings without error. I don't do this at work as much as I used to, so sometimes I switch to a TLK keyboard for more desk space.