The usual one-offs
Fat and food in the kitchen, hair and soap in the bathroom. Annoying, but a straightforward clear and you're done.
When it keeps happening
That points to something structural: a build-up of grease or scale narrowing the pipe, tree roots getting in at a joint, a section laid with the wrong fall so water sits and debris settles, or a partial collapse. Clearing the blockage fixes today. Finding the cause fixes it for good.
What we do about it
We clear it, then we check why it went in the first place, rather than just getting it flowing and disappearing. That's the difference between a fix and a repeat call-out.
Keeping it clear afterwards
A few habits save you a lot of grief. Keep fat and food scraps out of the kitchen sink, they set like concrete further down. Pop a guard over the plughole to catch hair in the bathroom. Run the hot tap for a bit after washing up. And whatever the packaging says, don't flush wipes. They don't break down, and they're behind a huge share of the blockages we clear.