Yes, pruning it hard after planting helps the plant push out more stems from the crown as well as allows the root system to get established.

There are many posts about pruning newly planted clematis. Here is one that came up when I searched using the search space below.

Here is a link that might be useful: Pruning newly planted clematis

Thanks, very helpful, but they seem to confirm my understanding that the plant needs to be pruned in early spring. I've also been watching YouTube videos of seemingly experienced gardeners transplanting new plants from nursery pots but not pruning back. Hence the questions whether its a) necessary to prune even a newly bought plant and b) okay to prune when hot weather is already here.

I prune all Clematis back, hard, when I plant them regardless of when during the year that I plant them.

Based on my experience with not pruning the first ones that I planted over a decade ago, I always recommend hard pruning with planting...