Lishy Yep, as mentioned, this is my preference to reduce risk of issue and reduce latency. Everyone will have different tolerance. Everyone will have different equipment and it will all work consistently and predictably, until it doesn't. Some of this also comes down to how much you trust Apple to not 'mess with' it's iOS stack in the iPad given how critical it becomes once you go down this path. My preference it to remove them from the equation.
BT latency and CME WIDI latency are a very data driven decision. If you are just using MIDI commands to change patches at the start of a song, then 7-10ms will have zero impact. If you are sending multiple MIDI commands mid-song for patch changes then that latency may have an impact.
The other thing, and this was specific to having the CME WIDI stuff in my setup, that made me just decide to disable iOS BT was the simple fact that when initially setting up the CME WIDI gear, you use the WIDI app to update firmware and configure them. This requires having BT enabled and pairing the WIDI devices to the iPad via BT. At home when adding a lot of new songs into ST3 I had a BT keyboard paired to the same iPad. Twice, I have been caught out at soundcheck/rehearsal with the WIDI stuff just 'not working' (i.e. not communicating with each other in their 'closed network'). It was entirely my fault - I had left BT enabled on the iPad from using the BT keyboard, and so the WIDI devices when powered up had re-connected to the iPad! X mins of hair-pulling and troubleshooting later, having reliased the problem, I just decided that the best way to avoid that situation was to not use iPad BT. Ever.
Now, yes, I could've un-paired the WIDI devices from the iPad, but then when I have to re-configure or update them, then I have to re-pair them all over again before I configure/update. Equally, could I have used a different tablet from m,y ST3 tablet to do all the CME device config? Yep. Still, not using BT on the iPad was my preferred path.
On top of that, the H4 is like a swiss-army knife, covering almost all scenarios, including what happens if someone loses a WIDI Master on their devices, or it breaks. No problem, 1 long physical MIDI cable and we're up and running again.
It also saved my bacon recently with it's MIDI filtering capability, which I never expected to use. We use our Behringer X32 as an IEM rig, but for a small event we did, it was easy to just turn it into IEM + FoH. One of the guitar effects unit I automate is on MIDI Channel 3, and I was automating our X32's effects on MIDI Ch 2. What I have never factored in was that the X32 is hard-coded to listen on MIDI Ch 1-6 for a bunch of basic fader operations. The first time we used our setup for a small event where it was also running FoH, the sound guy said "hey, one of your vocal mics keeps hard-panning to the Left at the start of most songs". Long story short, the MIDI commands intended for the guitar effects was also applying to the the panning control of a vocal channel on the X32! We'd never noticed as we didn't normally use the X32 for anything except IEM mix. So, quick fix was to go into the H4 and filter all MIDI info from going to MIDI Ch3 from the H4 MIDI out port connected to the X32. Problem solved. Obviously, long term fix is to change MIDI channel of guitar effects unit away from Ch3, but I'd need to edit all of my ST3 lyric sheets to do that, so that is a bigger "later" job.
You never know when you are going to need these sorts of capabilities.. until you do!