Getting a pet during a PhD
I bought a cat recently - I'm in the 4th year of my PhD, but I wish I had done it sooner. Particularly if you are working at a very high intensity, a pet provides 3 incredibly useful things:


A reason to go home. Many students, particularly international PhD students working at top-tier institutions where 18hr work days is not uncommon, tend to spend their entire life at work - after all there's nothing else to do. If you have a particularly one-sided work-life balance, a pet will force you to break up your day into work time and home time.
Time management skills. Before I had a pet, I would go to sleep when I was too tired to continue working, and so it doesn't really matter when I go to bed or when I wake up, so long as that period of time spent asleep is short. However, doing this for several years can enforce some pretty bad habits! With no strong circadian rhythm and poor eating schedules, you get worn out faster. Having a pet forces you to adopt a healthier schedule, for your pet's sake. New mothers/fathers often say the same thing, although a pet is certainly less work. It's not just sleep though, it filters down into everything you do - because you're responsible for two now.
Perspective. If the other two were wishy-washy answers, this one certainly is - however it's also the most important. I don't know about other pets, but cat's don't live all that long, depending on the breed. Mine has about 10 years, which means for every day I am alive, my cat burns up 7 or 8. 'Is he getting the most out of his life?' quickly becomes 'am I getting the most out of my life?'. Another similar but slightly different emotion that you get when you are the only person responsible for something else is, "am I being responsible with his life?". If I was to get hit by a bus today, there's a good chance the cat would also perish. Asking yourself how responsible a pet-parent you are, forces you to ask yourself how responsible you are being with your own life too.


There are obviously a bunch of practical reasons like time, energy and money (although honestly its not so bad), but im sure you have considered all those things already.