I agree if you're not strapped for cash, especially if you're on your feet and shooting subjects over a vast range of distances where you can't predict if or when you'd need to change lenses.
I don't regret selling my old body when upgrading but I do now realise it would have been nice to keep hold of it to put on a wider angle lens while keeping the long telephoto on my main body.
DSLRs: Canon EOS 7D Mark II, Canon EOS 70D
CSC: Canon EOS M3
Lenses: Canon EF-S 15-85mm f/3.5-5.6 IS USM, EF 50mm f/1.8 II, EF 100-400mm f/4.5-5.6L IS USM, Canon EF-M 18-55mm f/3.5-5.6 IS STM, Canon EF-M 22mm f/2.0 STM