We always recommend fitting a new consumer unit if you have an old fuse box as the old fuse box’s main function was to prevent your property from catching fire if there was a fault. If you happened to be the cause of an electrical fault (i.e. you suffered an electric shock) your fuse board would not even get near to blowing a fuse.
Modern consumer units with Miniature Circuit Breakers (MCB) and Residual Current Devices (RCD) offer two layers of protection on your installation. An MCB will protect against overloading and the RCD will trip out if there is a minute imbalance between the live and neutral circuits.
To put into context, if you think an old fuse board with rewireable fuses is perfectly adequate, and that there’s no reason to change it for something more modern, then ask yourself this… Do you still drive around in an old classic car, with drum brakes all round, with no brake servo let alone ABS,, and running on radial tyres?
That car might still work perfectly well, in the same way than an old fuse board might, but ask that old car to stop with modern fast moving traffic, on a wet dark night in rush hour on the M25, and you’ll probably discover that you’ll be having close acquaintances with the car in front’s bumper!
Older styled fuse boards cannot react in the same time that a modern consumer unit can.