You don't need one but it can make things very much easier.
In any difficult situation it makes sense to get specialist advice from an expert that knows what they are talking about.
And that doesn't mean google or a mate in the pub.
If you have separated from your spouse or partner the last thing you will want to do is sit in front of a lawyer having to go through things with them in their office. So why would you do that?
If you have separated, you are not alone in not knowing where you stand and not knowing how to even begin to sort things out - children, division of assets, ongoing financial support.
Few in that situation do know where they stand or what to do.
A good family lawyer will not inflame the situation. They will try to make it easier for you by removing uncertainty and giving you options. They will know what the choices are and how best to go about sorting everything out.
A detailed first meeting is a good start; and you can discuss with your lawyer what further work needs done and how much it is likely to cost.
The approach can then be tailored to what you want.
Good advice should make a painful situation more manageable and a bit easier.