In order to answer this, we really need to recognise what ISOFIX is, and it’s a standard. It is known as the international standard for attachment points for child safety seats in passenger cars.
It’s worth noting that ISOFIX is not just a standard for the UK, it also exists in other countries and is known by different names.
LATCH – United States
LAUS / CANFIX – Canada
The basic principle behind ISOFIX is that there is a minimum specification required to be built into cars to enable ISOFIX seats, this ensures both a universal connection and a higher requirement for safety than a seat belted baby car seat. The ISOFIX standard is designed for groups 0/0+ and group 1 seats, anything larger is referred to as ISOFIT.
Please note that there are subtle differences between ISOFIX, LATCH & CANFIX, so it’s strongly recommended that you do not import, but buy the baby car seat you need within the country you live in, to ensure correct fitting.
Within the UK a good ISOFIX base will usually cost you between £100-£200 and will probably last you the length of your requirement (Group 0-1). Have a look below at some of the ones found on Amazon.
Overall though, the reason they’re important is because they are made to meet a high standard of safety which is promoted by all areas of the industries involved. They’re not essential and not all cars and baby seats are capable of using ISOFIX but for the ones that can, it’s recommended that you take advantage of this level of security.
For further information, please see the wikipedia page below.