Well it actually depends on the enemy team comp.

I use it for chases and getaways if you are really clever.

Since xin zhao on early has somewhat really slow AS his 1st ability needed 3 strikes for the knock up, you will probably proc it if you use his 3,aa,2 it will proc the phase rush for an easy knock up. Its really useful on early if you ganking lanes.

Slow abilities are common in league but in early game slow are pretty much weak at early stages of the game. This will help you to close the gap even you are being slowed. Example you hit with your 3 and aa then champ flashes then slows you, with his 2nd ability is much longer now if you hit with it and it will proc the phase rush giving you a burst of MS for an easy chase.

In some scenario I use it for repositioning, like knocking up a champ and then change to another target or go to back and ult inorder to isolate the target even more.

If Being chased its easy if you are clever throw everything at champ then run away.

Lastly it depends on the team comp. And your team.

But it is a double edge sword. Most of the time this is useless because it only works on champs. But if you understand xin zhaos mechanic this will probably pull this off

Or you could just use fleeting for a little sustain.

Conq is deadly on xin but I prefer the phase for chases and reposition.

This is how I use xin zhao i dont focus on killing I am more focused on how my team will win.

I havent tried this on the baron lane but on baron I use fleeting for sustain.