Saving also buys you something more valuable - some peace of mind. You might at some point find yourself in need of a significant amount of money quickly (new boiler, car repairs, whatever) and knowing that you could cover it immediately from savings is a good thing.
A few hundred quid a month is a few thousand quid a year. If you really have no use for it at all, just save it. Maybe in 10 years time you'll decide you want to buy an impractical car just for jollies and spend £5K on tires and fuel having some fun with it. Or maybe you'll change jobs and decide you want to go on holiday for a couple of months in between. Or maybe you'll want new carpets and a conservatory. Or whatever.
Like pretty much everybody, you're not good at assessing the value of multiple small (to you) amounts. You see a few hundred quid, but it's actually a lot more. For example, £300 a month for 20 years is £72,000 even without any interest. It's easy to see the £300. It's much less easy to see the £72,000. It's the same way that "free to play" games make loads of money. It's only £2 for some stuff. That's almost no money at all! Not even noticeable, so you spend £2...and you spend £2...and one day you find that you've spent £50 on the game.
You don't have to use all your income. Your employer won't reduce your "budget" next year if you don't use it all. If you don't need it, don't use it. Stash it away and let it accumulate for unforeseen circumstances.
I now do that. On a smaller scale because I'm poor, but it's still very useful. For example, I spent ~£1200 on my main toy this year. That's more than a month's income for me, but I could spend the money and not care because it was surplus savings (i.e. above what I like to keep as a buffer for unexpected necessary expenses).
