Gravel driveways are one of the most popular choices for driveways and hard landscaping in the UK, and it's easy to see why. It's cheap, easy to lay, low maintenance and looks good, particularly in country settings or in towns where it matches the predominant stone and brick colouring of the area. There's an immense choice of size, colour and texture, so it's a good choice for resurfacing.
The crunch of gravel under a car's wheels is very satisfying and can also act as a defensive measure, alerting you to uninvited guests. On the downside though, you can't use it on a site that has any gradient to speak of, it needs regular top-up resurfacing, and can be tricky to keep in place.
You need to consider the use that the gravel will have to deal with. For a garden path, patio or other landscaping, you can be far more creative with mixing colours and patterns than for a gravel driveway. Any multi-coloured layout on a drive will quickly lose its coherence as the wheels of the cars will spit the gravels all over the place, breaking down the barriers between the different colours. You need also to consider how comfortable a gravel might be to walk on; slate mulch, if it's coarse, is not likely to be particularly good in this capacity.
For a long gravel driveway it might be worth considering self-binding gravels. These are effectively supplied in a form that's dirtier than the usual gravel, but the dirt is very useful. It's actually the smaller particles, the dust (known as 'fines' in the trade) that is cleaned from the gravel that is sold at garden centres. The fines are left in with the stones for these self-binding gravels and in some products they even have more fines added.