Andy Sellick, Senior frontend developer, GOV.UK:
The main disadvantage of using jQuery is that it has to be included in the page assets, which can slow down how quickly a site loads. GOV.UK’s pages vary in size, but the homepage is around 246 kB – 32 kB (13%) of which was jQuery. That’s not a huge amount, but it’s worth considering the performance impact, especially for users on low-specification devices.How and why we removed jQuery from gov.uk
And here’s the impact it had on performance after jQuery was removed.