We do a mixture. We don't do any plumbing ourselves. OH is happy to change light switches/sockets (i.e. take off if we're decorating or change a single socket to a double etc) and change ceiling lights, etc. Likewise, he'll remove/replace a door, door locks, etc but wouldn't fit a new door himself.
Re decorating, we fully decorated (wallpaper, painting etc) ourselves, inside and out when we bought our house (inc the hall, landing and staircase wallpapering which was a challenge). Then we started having decorators in to change rooms etc., but never really happy with them (despite them being qualified/experienced etc), so have gone back to doing our own again.
Gardening has also been mixed. Again, at first we did everything we could ourselves even felled a couple of short-ish trees. But then got a gardener for grass cutting and pruning etc but only had him a year or two - not really happy as he'd just randomly hack some shrubs and ignore others so the garden became quite messy and unsightly, so we're back to doing it ourselves.
We also got a cleaning firm to come and power wash the patios, decking, etc., but they did a shoddy job too, so we've bought our own Karcher and now do it ourselves.
So, really, our approach is to let the qualified pros (Gas safe plumber and qualified Electrician) to do the things which are potentially dangerous, but do virtually everything else ourselves. Often cheaper to buy the tools you need and invest a bit of time to get a better result.