In general, typographers try to avoid ending a page with a short fragment of a paragraph or starting a page with the last small part of a paragraph. These are called widows and orphans. They are bad because they look poor and make the document harder to read.
This is not a problem that you should really worry about in legal writing. Most legal documents are written in Word, which has automatic functions dealing with how paragraphs are split. These generally produce an acceptable result and tribunals expect functional documents, not beautiful ones.
There are, however, two situations where manually tweaking can help just enough to make it worth doing.
The first is when quoting legislation. To Word a series of sections in a statute looks like a sequence of short paragraphs, so it is happy to split them over a page break. This is undesirable. To a reader, the series of sections is one paragraph, which they want to see as a whole. Indeed, splitting the legislation over two pages is likely to create more problems than any other type of page break. Legislation is something you often need to read carefully and more than once. Having to flip between pages makes this harder. Even if there is no real choice but to go over two pages, it is worth trying to make the break at some sensible point.
The second situation is where the content around the break produces an unintentionally confusing or humorous result.
For example, if you are representing Mr Jones you might write ‘Mr Smith then said that Mr Jones stole £5,000 and that was an act of misconduct.’ But an unfortunate page break might mean that you appear to start a new paragraph with ‘Mr Jones stole £5,000 and…’ Even if this is unlikely to cause real confusion, it is worth avoiding for appearances sake.
To fix these problems, just manually insert a page break in a more sensible place or rewrite the problematic sentence.
Obviously, these sorts of manual adjustments should be the last thing you do before finalising your document. Otherwise, subsequent changes are likely to shift the page breaks and disrupt all your careful work.