Good questions, I probably should have explained but my post was already a bit long 
For me personally, I use a London one for business (I also have an 03 number with tel2 that I use for business) and one local to my home-town so that friends & relatives who use landlines can call me in a way that they’re comfortable & familiar with, also, some of them are charged more to call a mobile number so a landline helps them out a bit.
All of these numbers come straight through to a sip client on my mobile phone (provided I have an internet connection which I usually do or I’ve set up some fancy handling stuff to make sure that people don’t just get bounced) where I can easily answer them no matter where I am 
For the business one I also have some stuff set up through the API so that it can go through to multiple people with as little friction for the caller as possible, we all work from home so we can all have one.
Oooh, I hadn’t seen vyke, looks like what I’m doing but with less manual work and it’s definitely a good idea to split numbers, probably worth doing that myself considering how many I have 
Edit: Oh dear, that reminds me, I’ve also got a US (New York) one through Google Voice…