Here are a couple of reasons why you might want to hire a land surveyor.
To ensure you don't make changes to features that don't belong to you
One important reason to use this professional's service is that they could help you to avoid the consequences that could come with altering features of the land that don't actually belong to you. If for example, you don't hire a land surveyor and, when landscaping your new property, you decide to remove a tree that turns out to be owned by your neighbour, you could end up dealing with a lot of issues.
Firstly, that neighbour might want you to reimburse them for the tree you removed or they might want you to arrange for a new tree to be planted in its place. Furthermore, if the tree in question was a protected tree that should not have been removed without prior permission from the local council, you might incur a fine. Having a land surveyor spend a few hours on your property and asking them to confirm which features are within or beyond its boundaries could allow you to avoid all of this, whilst also ensuring that you don't waste your own time and financial resources altering features that do not belong to you.
To find out if any neighbour has the right to access parts of the property
As part of their work, most land surveyors will check to see if anyone has a right of way across their clients' properties. This information could be invaluable to you in the future. If you don't use a land surveyor's services and a neighbour does have a right of way across your land, which you're unaware of, you could inadvertently put yourself in some very stressful situations. For example, if you spot a neighbour using your garden path and then confront them in an angry manner about it, when they have a legal right to use that path, you could find yourself very embarrassed and might end up having an argument with them that would have been avoidable had you hired a land surveyor.
Similarly, if you're unaware of your neighbour's right to access a particular area of your property and you then make changes to the property that make it impossible for them to use that area (for example, if they have a legal right to use your garden path and you then remove that path and plant shrubs in that area), you might, upon being informed of your error, need to replace the garden path, in which case all of the money and effort you utilised to make these changes would have been for nothing.