Bleach bath misconceptions?

There are no hard and fast rules, it depends what you want to achieve. A bleach bath is just diluted bleach.

Applying to wet hair will dilute it slightly more, but also make it easier to get the mixture onto the hair quickly.
I use a bleach bath when i want a small amount of lift all over, the mix can be rubbed through the hair because of the shampoo. It doesn't need to be applied precisely with a tint brush, so it is much quicker to apply.

If I want a more controlled amount of lift, or i just want it on certain sections, I would use a low vol bleach. 15 or 10 vol straight, applied precisely with a tint brush to each section.

Using 10 vol diluted with shampoo is going to give very minimal lift, it would be more of a stain removal strength.
Also remember that bleach damage is cumulative, it isn't a given that you will be able to lighten further after a week. If the condition of your hair is compromised, do a strand test before proceeding with any further processing.

@Wicked Pixie Thank you very much!

Yeah I had a feeling using it on wet hair makes it a lot easier and quicker to apply for an all over lift. Until recently my hair was slightly uneven in colour, with the inside layers darker than the outside, so I've only used 30vol diluted to 15vol to bleach bath certain areas at a time on dry hair.

Oh also, I just used 10vol as an example, I haven't actually used 10 as I thought it would be too weak. But if that low of a volume can be used as a stain removal, that sounds good.

So does this mean it makes no difference if I dilute 30 vol 1.1 to create 15 compared to used 15 straight?

I have never actually tested 15 vol bleach against a 30 vol bleach bath, but I would imagine you would get slightly more lift with the straight bleach. (I could be wrong, i want to compare them now lol)
I have never left a bleach bath mix on for as long as straight bleach either, I use them for 15-20 minutes only.
What are you actually trying to achieve? What colour is your hair now and your end goal?

Well I was interested partly for my own curiosity but also, I'm currently aiming for even inside of a banana blonde so I can dye my hair silver or lilac (or something pastel) over the summer. Currently the main bulk of my hair is a pretty even yellow blonde (maybe level 8/9). However I have a serious regrowth situation. I have about an inch regrowth on the top layer, but on the underside layers where I've been lazy, I've got about 2 inches. I was thinking of doing a standard bleach 30vol on my roots (I strand tested this earlier) it reached a sort of gold-yellow gold (maybe level 7/8). Then after at least a month I could start bleach bathing until it matches the rest of my hair, and then finally gradually bleach bath until it's lightest blonde.

But yeah before I continued to bleach bath I wanted to double check I was doing it right and not harming my hair (well, as little harm as possible whilst bleaching). So far my hair is in very good condition. Also, so far I've never bleached bath regularly, like one a week. I've probably only done it like once a month.