I recently started learning texturing and uv mapping

I am to trying to unfold a model

The original UV layout of the model is a mess and in the top right square.

I unwrapped a portion of the object and moved it to the empty areas of the UV texture editor

Then I go and unwrap another portion of the model. As soon as I click unfold for the 2nd part of the model, both manually created UV maps move into the top right part of the grid where the mess is.

So i need to know what setting stops the UV maps from realigning into the top square after every unfold.

I have looked through options and changed some options such as

Edit UVs>Layout to no result.

I deleted the orignal UV maps created by Maya to empty up the grid, but it still moves them to the first grid and now it also rescales them to fit the top right grid.

So another few questions that I need to confirm:

Does rescaling your UV maps do anything because the tutorial said to leave them alone?
Does deleting the original uv map created by Maya affect anything? Is it used to compare the old to new to see if everything is working?