No it is not always better. For example labor for woodworking and carpentry in my country is expensive.
A small kit of Abatron - 12 oz epoxy penetrant and 12 oz of epoxy putty - is $45. Replacing a clapboard is done by simply removing a couple of nails and sliding in a new clapboard. It's a lot less work. (I've used Abatron - it has its place.)
That clapboard was completely rotted. An attempt at patching it will only last a few years, at most. A new, properly painted (six sides) clapboard will last over forty years.
This is true for a clapboard, but not for a wood window or doorframe
I've replaced some rotted windowsills. You can patch them up to a point, but it's a losing game. In particular, replace any rotted casing or casing which is splitting at the bottom due to dry rot. You have to keep the water out. Prime new casing pieces six sides and be sure to flash the tops and caulk the verticals against the clapboards.
In most cases, it’s better to just replace the wood.