For me it came down to relearning to typing in numbers, as I was very used to using the numberpad for inputting numbers. The first week of having my new mechanical keyboard I found myself automatically reaching for the numpad when wanting to enter numbers, so that was a bit of an annoyance. But as with everything muscle memory related, I soon readjusted and started using the number row, now I don't think there is much need for the numberpad for the kind of input I do with it. Or rather used to do with it.
That might change in the future, and then I will be more than likely to buy a numpad that I will pull out when need be.
The shorter travel distance is not only for gaming, but day-to-day use puts less strain on you having to move your arm that extra length.
For me it is also a lot more comfortable having a centered keyboard, and with the 100% keyboards I never felt I really got that (at least with the ones I have). Admittedly I didn't really know what was causing my discomfort until I started using my tenkeyless, but now that I do, I am sure I will find it difficult to use a 100% for longer periods of time.
Some popular band once had a song called All the small things. I am sure the reasons for you wanting a keyboard will be different from mine, but think about what you like, and remember that one keyboard isn't the end of the line
/rant