"Under inflated tyres will increase stopping distances and affect your vehicle’s handling so that collisions are more likely; Under inflated tyres will flex more and get hotter, making sudden tyre failure – blowouts – more likely; Under or over inflation increases tyre wear so you’ll have to buy new tyres more often; Under inflation increases your tyre’s rolling resistance which means higher fuel consumption"
From https://www.theaa.com/driving-advice/safety/tyre-pressures
"Under inflated tyres will increase stopping distances and affect your vehicle’s handling so that collisions are more likely; Under inflated tyres will flex more and get hotter, making sudden tyre failure – blowouts – more likely; Under or over inflation increases tyre wear so you’ll have to buy new tyres more often; Under inflation increases your tyre’s rolling resistance which means higher fuel consumption"